Originally Posted by irishcrusader95
there use of combined arm tactics was the key. the pike men held off any cavalry assult while the arqubusers fired from the protection of the square. i would be interested to know if whether other countries ever addopted it?
After the success of the Spanish army in the Italian Wars, the combined formations of arquebusers(later musketeer) and pikemen and other melee combatants became a sort of standard model, adopted by pretty much the most important European states in order to keep up with the mighty military machine of the Spanish Empire.
Of course, these formations were not original tercios(they had minor or major differences compared to the Spanish ones) but were based around the same successful method of fighting based on the collaboration between shooters and pikemen.
A standard Spanish tercio fighting in Flanders(1636) was composed by 31,5% of pikemen and 68% of shooters(11% of whom were using arquebusers)
In 1612, several French formations were still formed by 50% of pikemen and by the other 50% of shooters.
In the 1620s, the army of the great Gustavus Adolphus still had companies formed by 43,5% of pikemen.
One of the few states really in step with the Spanish military organization was the Republic of Venice: a 1620 military ordinance ordered the formation of military units formed by 66% of musketeers and by the remaining 32% of pikemen; but of course we can't compare the military importante of the XVII century Venetian army with the power of the Habsburg monarchy.
The combination of shooters and pikeme provided a good decree of flexibility, with tercios successfully used in both offensive and defensive manoeuvres.
We can observe by the numbers the great emphasis on firepower, one of the main reasons that made the success of the Spanish tercio.
The other factor was the great infantry tradition: Spanish infantrymen were famous for their great discipline and cohesiveness and the entire army was meant to orbit around the tercios, with the cavalry subordinate to the infantry, while in other European countries, serving on foot was still considered "inferior".
Moreover, the Spanish tercios had a lower number of foreign mercenaries, with a good number of men coming from their countries under the direct rule of the Habsburg crown, with a comradeship unknown to other countries.
The Spanish infantry tradition proved also instrumental for creating a successful pool of able general, skilled in coordinating the efforts of the various body forming the army.
Starting from Gonzalo Fernandez the Cordoba(the creator of the Colunella, the progenitor of the Tercio) and Fernando Francesco d'Avalos(the man who picked up Gonzalo's legacy) we can see how the organization and the performance of the Spanish army in the battlefield was based on the cohesion of infantry,artillery and light/heavy cavalry, with the establishment of mixed units. On the other hand, most XVI century armies were still organized in "battles"(a medieval legacy): with a battle consisting only of heavy cavalrymen, a battle of pikemen and so on.
If we take a look at the battle that established the military dominance of the Spanish army during the fist decades of the XVI century we can see how infantry was the key:
Cerignola(1503) won by the arquebusers
Bicocca(1522) won by the coordination between infantry and cavalry
Sesia(1524) won by arquebusers, used together with the light cavalry(one of the earliest examples of mounted firearms shooters)
Pavia(1525) won by arquebusers and musketeers
The Spanish tradition of excellent infantry commander continued up until their defeat at Rocroi: Alessandro Farnese and Francisco de Melo(the man who lost at Rocroi) all proved to be outstanding generals.