While in popular media, dominated by American productions, WW2 is clearly seem as a war won by the US, in internet forums the focus is more on the Eastern front, seem as the decisive front of the war. However WW2 was a very large and complex war with many factors involved. Both the US, the Soviet Union and the British Empire played decisive roles in winning the largest and most destructive war in history. German grand strategy
Most military historians consider that Germany began WW2 in September 1939 by accident. Hitler probably though that UK and France were bluffing when they issued their ultimatum and he was only trying to fortify Germany's position, by annexing Austria, Czechoslovakia and Poland, Germany was increasing it's resource base in preparation for a world war. However, the plan backfired and France and the UK declared war on Germany.
Germany's strategic position at the beginning of the war was not very good. They were at war with France and UK, with had a total population of 90 million plus Canada and Australia, industrialized territories with another 17 million inhabitants that the UK could draw manpower from. Also, the highly industrialized countries of Belgium and Netherlands, with 18 million inhabitants, were officially neutral but were in practice Germany's enemies, since they would have to get thought these countries to attack France. So Germany was an industrialized country of 79 million inhabitants, compared to a population of 125 million inhabitants of it's industrialized enemies.
Germany's access to natural resources was also blocked by the French and British navies, so Germany was running against the clock here, if the war dragged for too long Germany would be without the raw materials to continue the war and would be forced to surrender.
In September 1939 Germany attacked Poland with 60% of the Wehrmacht ground forces, about 60 divisions, versus 40 poorly equipped Polish divisions. Each German division had 5 times the firepower (measured in weight of projectiles fired by all it's artillery pieces) of each Polish division. In 17 days the Polish front collapsed completely and in 35 days all Polish resistance was mopped up. The 60 German divisions were consuming nearly 3,000 tons of ammunition per day during their "Polish expedition". It was a very large strategic offensive and resulted in rather heavy German casualties, at 50,000 men lost in about a month.
Since the bulk of the Wehrmacht power was engaged in Poland, German commanders even commented to the Allies, after the war was over, that they could have won in September 1939 if they attacked Germany with everything. Instead, the Allies decided to use the same strategy they had already used to defeat Germany in WW1: stay on the strategic defensive until the German army is exhausted and the raw materials mostly run out and them attack and defeat Germany. However, Germany carefully prepared their attack to correct the errors of the past. The Allies still had greater resources in May 1940, they outnumbered the Germans slightly in terms of manpower, artillery pieces, tanks and aircraft.
The attack in May-June 1940 was the greatest military victory in human history. Germany was able to achieve near total victory over the powerful Allied coalition at a comparatively minimum cost. It was Germany's most concentrated effort during the war: 90% of all divisions available to the Wehrmacht were employed in the Battle of France. Average daily ammunition consumption during the 40 days offensive of was 5,000 tons. All guns were blazing and Germany gave maximum effort in their attack. As a result, they managed to defeat and occupy France, Netherlands and Belgium and to kick the BEF out of the continent. Total Allied losses in strategic terms were the 6 million men in the French army that surrendered and 1.2 million Belgians and Dutch forces.
After this massive victory Germany became the master of an empire containing France, Belgium, Netherlands, Denmark, Germany, Norway, Austria, Czechoslovakia and most of Poland. These territories had about 30% of the world's GNP and industrial production in 1939. And Germany was only able to last until 1945 thanks to the massive resources in these territories, which they exploited to the maximum during the war: from July 1940 to July 1944, France paid 40% of their national product to Germany in forms of occupation taxes.
The natural resource problem, however, continued, while Germany had massive human and industrial resources, they lacked the raw materials to make full utilization of these resources. The most acute problem was oil, which Germany lacked and couldn't import from abroad due to the British blockade (and Germany also lacked a powerful navy in WW2, able to threaten the Royal Navy).
After the battle of France Hitler tried to force the British into surrender by terror bombing of their cities. After 60,000 metric tons of bombs dropped, half a million buildings razed, tens of thousands of deaths and the loss of 1,100 bombers and 650 fighters in the effort, British resolve to continue the war became not weaker but stronger while Hitler lost interest in engaging the UK in war, cancelling the amphibious invasion of UK (which probably wouldn't have worked out well, considering that Germany lacked adequate means of transporting a large army across the channel).
Instead, to solve Germany's natural resource problem, they planned to conquer the vast territories of the Soviet Union, which were full of oil and other critical natural resources that Germany needed. Given the spectacular performance of the German army in 1939 and 1940, easily destroying anything in it's path, the bad performance of the Red Army in the winter war, and the vast technological and industrial resources under German control after the defeat of France, it was expected that Germany would be able to destroy the USSR in a matter of a few months. German strategic planners expected 500,000 German casualties in a 4 month campaign to defeat and conquer the USSR.
For Operation Barbarossa, Germany allocated 152 divisions out of the 210 divisions in the army, so 69% of the German army was allocated to defeat the USSR, instead of 90% in the case of France, the other 58 divisions would stay in Western Europe, in order to garrison the vast domains of the newly formed German Empire. Germany also did not increase ammunition production for Operation Barbarossa, because they though that the USSR would be defeated quickly and easily, not requiring a long and sustained war effort:
German arms and ammunition production increased greatly from 9/1939 to 6/1940, and after the defeat of France it decreased greatly. By 1941 Germany was producing small quantities of ammunition, even during the invasion of the USSR, given that they expected that the army would consume only 4 months worth of supply.
The German planners did not expect the USSR to be able to fight a large scale war against Germany, because of the rather easy defeat of Russia in WW1 and the fact that despite Stalin's industrialization efforts, even in 1937, 57% of the labor force of the Soviet Union was still employed in agriculture and the bulk of the population of the USSR resided in huts in the countryside. So they though that 152 divisions at full strength of the best army in the world, including 20 armored divisions and 12 motorized divisions, would be more than enough to defeat and conquer this vast country.
After conquering the USSR, Germany would be able to focus exclusively on defeating the US and the UK in a war for global supremacy. This war would involve mostly the airforce and the navy, so Germany would demobilize most of their army and put their manpower to work into the aircraft plants and shipyards. US grand strategy
The United States was already the largest industrial economy in the world since the late 19th century, when it's industrial production surpassed the UK's. By 1939 the US had around 35% of the world's industrial production and was by far the strongest economy on the planet, both in terms of productivity and total production. Over the course of the war the US would use their vast material resources with decisive impact over the course of the war.
The US began to prepare for war with Germany in September 1939, when Germany attacked Poland. The US began total military mobilization in June 1940, when France surrendered and the US strategists knew that US help would be needed to defeat Germany. They were already sending vast quantities of supplies to the UK in 1940 and when Germany attacked the USSR the US decided to directly enter the war. Probably the two main reasons were:
1 - If the USSR is defeated, Germany would gain control over the whole of European continent and it would be almost impossible to defeat it.
2 - With the bulk of the German army in the USSR, to defeat the rest of the Wehrmacht would be much easier.
In September 1941 it was already ordered that all US Navy ships to shoot German vessels on sign and the US armed forces, which had a strength of 200,000 men in 1939, were already expanded to 1,400,000 men by December 1941. Large scale industrial and military mobilization was well underway when the US formally entered the war. The only thing the US government needed was a psychological reason to convince the population to support total war against Germany. To do so the US cut Japan's oil supply in August, 1941. Japan was Germany's ally and the US hoped that this would force Japan to attack the US which would trigger a German declaration of war against the US, which was what exactly happened.
US propaganda also focused on linking the German and Japanese enemies, to form a unified image of a German/Japanese enemies:
But in the truth is that only Germany was a real threat to the US: Japan had a national product of 8% of the US's size in 1939. Equivalent to the proportion of the current US GNP that Mexico holds. Japanese production of explosives, the item that determines the total firepower available to it's armed forces, was ca. 65,000 metric tons a year while American production was well over 1 million tons by 1943-1944.
So, the US would concentrate first on defeating Germany and after they had defeated Germany, they would finish off Japan and other Axis countries. To defeat Germany the US first sent rivers of money and supplies to the UK and the USSR:
For example, in 1943 the total military expenditures of the USSR were equivalent to 76% of their national product, but the US paid for 18% while the USSR had to finance "only" the 58% of it's national product in terms of military expenditures. The US was directly paying for 24% of all USSR's military expenditures in 1943 and 18% of the UK's military expenditures.
Without US help, both the UK and the USSR would have been probably defeated by Germany. The UK would have been strangled by the U-boats, given that it was the American shipyards that produced the millions of tons of merchant ships that replaced the losses to the German submarines (German u-boats sank British merchant ships at several times the rate UK produced them, but the US produced ships even faster than Germany could sink them) and the USSR would have faced a larger enemy army with significantly smaller resources, given the critical state of the Eastern front from 1941 to 1943, it becomes hard to think how they would have survived even worse odds than those that historically occurred.
After helping the survival of the UK and the USSR, the US would concentrate on building an army capable of directly defeating Germany. The victory plan made in 1941 consisted of a plan of producing 150 billion dollars of munitions, including equipment and supplies, for the armed forces. That was nearly twice the annual national product of the United States (in relative terms, it would be a 25 trillion dollars plan today) and was the amount of munitions that the US strategic planners judged to be required to equip and supply a force capable of defeating Germany. Japanese strategy
The strategic planners in Japan were fully conscious of their limited industrial and technological resources if compared to the major European powers. They did not attack the US expecting that they would be able to defeat it alone in total war. No, the attacked the US in December 1941 because the Wehrmacht was on the gates of Moscow and therefore the Japanese strategic planners also hoped that the USSR would surrender over the next months and Germany would be able to turn all their guns into the west, forcing the US, UK and other western powers to concentrate fully on Germany.
Japan would take advantage of this situation in Europe to expand their empire in Asia. Capturing Belgian, French, Dutch, British and US colonies into their own colonial empire. The Japanese planners knew that they had limited chances of defeating the US if they had to fight it alone, they were not irrational and they were expecting even to have to lose some newly conquered colonial territories to the US in order to make a negotiated peace.
Japan's economic underdevelopment:
Notice that both Japan and the USSR had much lower levels of economic development than Germany, UK and the US, the three most technologically advanced countries in the world at the time of WW2. Opening the Eastern Front
In June 1941 Germany attacked the USSR with 3.1 million men distributed over 152 divisions. Of which, about 30 divisions were fully motorized and two thirds of these were armored. These motorized forces were the armored spearheads of the German army, designed to pierce the enemy front and to flank and encircle the enemy armies, reproducing the role of cavalry in Hannibal's victory in Cannae. The meat and potatoes of the German army consisted of infantry divisions, which had a table of organization strength of 9 infantry battalions and 4 artillery battalions each. These divisions represented the vast majority of the German firepower and inflicted the vast majority of the enemy casualties but had poor mobility. The role of infantry and armor in the Wehrmacht were analogous to infantry and cavalry in Alexander's army, the infantry divisions they were the anvil while the armored divisions were the hammer.
Over the first weeks of Barbarossa everything happened as planned. While consuming 4,500 tons of ammunition a day, the Wehrmacht advanced and whole Soviet armies were quickly encircled and destroyed and the German armies advanced by a third of the distance required to reach Moscow. But over the next weeks problems started to appear on the conduct of operations and the advance slowed down. These problems related both to Soviet resistance and to logistical problems of advancing the supply depots as quickly as the army. Eventually the German advance stopped after 1,200 kilometers of nearly continuous advance over a territory containing nearly 40% of the population of the Soviet Union. They had reached the limits of their supply lines, had suffered many casualties, which reduced the effectiveness of their divisions since casualties were usually for soldiers employed at the "tooth" of the army, thus losing 20% of the men would imply in a reduction of combat effectiveness greater than 20%, since these 20% would be the combat troops directly at the front. And the Soviet resistance was placing increased stress over the advancing German army. By the end of 1941, the Germans had lost over 800,000 men over 6.3 months of operations, the Operation Barbarossa had failed in knocking out the USSR in 4 months and the Red Army had lost over 4 million men, and territories containing 70 million inhabitants. Casualties were greater in the first months of the operation, as the winter came and the German armies outran their supply lines combat became less intensive:
The Soviet Union had survived the German attack at a huge cost of both manpower and territory. And the costs would only increase over the next months of the war. Given the huge number of Soviet losses the German strategists expected that the USSR was at their critical limits in Early 1942, they expected that the country would collapse at any time. And they were indeed at their limit: civilian consumption declined 70% from pre-war levels, food production declined by 60%, during the war the entire resources of the Soviet Union were allocated to the single goal of defeating the invading German forces in the Eastern front. Given that the USSR was a poorly developed economy their effort must be put in perspective: while the industrialized countries were cutting consumption of non-essential goods both the USSR and Japan had to cut their food consumption in order to pay for the war and both countries went hungry during WW2.
Over the course of the critical months from October 1941 to December 1942, the USSR was losing over 6 soldiers for each German casualty. The Wehrmacht was losing 90,000 men per month, an average loss rate that was perfectly replaceable, while the Red Army was losing over 560,000 men per month. The USSR was losing territory and was desperately trying to survive by mobilizing everything they had into the war effort. The other allies had their fingers crossed, hoping that the USSR would make it, while the Axis countries had their fingers crossed hoping that the USSR would collapse and Germany's resources could be employed in other fronts. German allocation of military resources
One thing to keep in mind is that Germany was always focusing on multiple fronts during the war. So they never could allocate the totality of their resources against the USSR. Even though the Eastern front was the largest and most important front of the entire war, it was far from being the only strategically relevant front. Germany had to produce 1,200 submarines at the same time they were invading the Soviet Union, to sink Allied merchant ships at the battle of the Atlantic.
In mid 1943 the German armed forces were organized as follows:
9,550,000 men in the Wehrmacht
- 7,000,000 in the army
--- 4,400,000 in 280 divisions of the field army
--- 2,600,000 in the reserve army*
- 1,750,000 in the airforce
- 800,000 in the navy
*units in training, involved in logistics and in the hospital.
Of the 280 divisions of the field army, 180 divisions were in the Eastern front and 100 divisions were in other fronts. This was in July 1943, when the Germans launched their last strategic offensive in the Eastern front. After July 1943 the proportion of German divisions employed in the Eastern front was gradually reduced. Of the airforce, about 50% of all units were allocated in the eastern front in mid 1943, which reduced to a gradually smaller proportion as the Anglo-American air forces bombed Germany. And 0% of the navy was employed in the eastern front. So, in mid 1943 the German manpower was allocated as follows:
1,500,000 men of the field army out of the Eastern front, implying in 900,000 men of the reserve army were also out of the Eastern front. Plus 1,400,000 men in the air force (most manning anti air batteries in the Reich and occupied territories) and 800,000 men in the navy. For a total of 4,600,000 men of the Wehrmacht not employed directly or indirectly in the Eastern front while there were ca. 4,900,000 men employed in the Eastern front, directly and indirectly. Of which ca. 2,750,000 men were directly at the frontlines.
From June 1941 to December 1942 the bulk of Germany's attention was directed at the eastern front. After the failure of Barbarossa the goal was the conquest of the oil producing Caucasus region. After the defeat of German forces in North Africa and the defeat at Stalingrad, the Germans gave up on the Caucasus and instead shifted their strategy to a purely defensive one. The oil that Germany consumed would have to be mostly the very expensive synthetic one with some Rumanian oil to help, the Germans would have to do miracles in order to defeat the United States, UK and the USSR with the 9 million tons of oil they had per year. The plan was to fortify the lines in the Eastern front while the U-boats would damage the logistics of the Western Allies and the Atlantic wall would protect the core of Germany's empire against amphibious invasions from the US and the UK.
In mid 1943 Anglo-American forces landed on the European continent. In Italy specifically, and Italy itself surrendered, a country with barely helped Germany now gave up when the Allies reached their territory. Now Germany had to place 25 divisions on the Italian peninsula, a force of 15% of the size of the army in the Eastern front, to contain the Anglo-American advance. This forced the Germans to cut their reinforcements for the Eastern front and to cancel any strategic offensive operations. Now the Germans would only lose territory to the USSR, as their resources had to be focused on fighting the Western Allies.
German manpower resources were always strained to the maximum during WW2. As Germany was a country of 81 million inhabitants in 1943 at war with the USSR, US and UK, countries with had a total population of 360 million, add 17 million for Canada and Australia and we have 387 million Allies versus 81 million Germans. To partially compensate for such terrible manpower odds the Germans used the manpower of the occupied territories to replace the conscripted manpower in the civilian economy:
Most of this manpower consisted of voluntary workers that worked in Germany due to the relatively high wages and the high demand for labor due to the lack of ethnic Germans in the labor force as many were conscripted. Still, even with the contribution of labor for occupied territories and inflicting 5-6 losses on the Soviets for each German loss, the German numbers in the Eastern front were decreasing in proportion to Soviet numbers. Why?
Germany mobilized a total of 17.9 million men in the war, the USSR mobilized 34 million. German manpower allocated to the Eastern front from June 1941 to December 1944 was 8.2 million (ca. 46% of the total manpower mobilized), Soviet manpower allocated to the Eastern front over the same period was 32.5 million (ca. 95% of total manpower mobilized). The difference was that Germany was fighting a multi front war while the USSR was fighting a single front war. Checkmate
In May 1943 the U-boat fleet was defeated, thanks to the fact that the Allies were able to broke the German codes and successfully engage and destroy more U-boats than the Germans were able to build. Adding the increasing American production of merchant ships in 1943 meant that by mid 1943 the Allies were able to increase their logistical capability over the Atlantic, which finally would enable a full scale strategic offensive in the core of the German Empire.
While the increasing number of strategic bombers, produced both by the UK and the US, and it's fighter escorts, meant that Germany was suffering increasingly intense bombings. By late 1944 the Allies were dropping 100,000 metric tons of bombs per month over Germany with was equivalent in destructive power to about 5-6 Hiroshima bombs dropped monthly over Germany. While strategic bombing failed to decrease German war production before mid 1944, it helped to reduce it's rate of increase and perhaps the most important contribution of strategic bombing was the destruction of the synthetic fuel plants in May 1944. The Luftwaffe was knocked out of the war that month as the aircraft fuel production was almost completely stopped and the increasing number of aircraft that Germany made per month in 1944 served nothing as they lacked the fuel to actually use these new aircraft. Also, increasing losses in air battle of the defense of the Reich imposed severe attrition over fighter pilots and therefore reduced the number of well trained pilots available and Germany lacked the fuel to train well more pilots.
By mid 1944 the Allies had succeeded in defeating the German airforce and the navy. The German armies were in the defensive and outnumbered in all fronts by a wide margin. German manpower was stretched beyond their limit. And in 6 June 1944 the US and the UK landed in massive numbers on Normandy. Over the next 80 days the Allies would land 2,060,000 men and 8,800 tanks in Northern France. A massive enemy army just had popped out when the Wehrmacht was already fighting to their limit and now they were completely overwhelmed. Germany was able to gather 600,000 men and 2,300 tanks to engage the Allied forces and they fought hard and well but were defeated by the impossible odds. While against Poland the Germans were able to fire 3,000 tons of ammunition per day, against the US forces in Normandy the Germans were only able to supply their forces with 480 tons of ammunition per day, while the US forces responded by firing over three times that ammunition tonnage back at the Germans. American losses from June 1944 to April 1945 were heavy, almost as heavy as the German losses in the Eastern front in 1942:
US manpower allocated to European Theater of operations:
By August 1944 the Allies had succeeded in breaking the German containment and the Germans had just lost France and Belgium, their most important occupied territories. While in the Eastern front the USSR was able to launch a massive offensive that encircled army group center and forced over twenty German divisions to surrender. Total German losses from June to September 1944 were over 1.3 million men. By late 1944 the Wehrmacht was facing impossible odds in all fronts:
2,100,000 Germans to 6,600,000 Soviets
1,000,000 Germans to 2,250,000 British and Americans
350,000 Germans to 800,000 Allies
In late 1944 and early 1945 the Wehrmacht tried some desperate offensives but these offensives did not have any sustainable effects at all on the Allied armies. In December 1944 the Germans attacked though the Ardennes with 350,000 men, against 130,000 American soldiers, initially they defeated these soldiers and managed to advance over 90 kilometers before the Allies reinforced the front with over 500,000 men, which they had to spare from other sections of the front and finally they managed to drive back the Germans to their initial positions after 40 days. Concluding
Germany lost WW2 simply because they failed to defeat the USSR in time to shift their resources against the growing strength of the Western Allies. The Allies had simply too much manpower and this was also reflected in armament production as the German factories lacked the labor to operate on two or three shifts while the US and Soviet industries were all running on two or three shifts. To survive the war Germany should have accepted the Soviet peace proposals, that were made in 1941 or in early 1943.