MacArthur’s warning to JFK about a land war in Asia is well known and the old general was in a position to know. Not only did he have his Korean experience to draw upon but he also had seen the impossibility of Japan’s effort to defeat and control China.
British Field Marshal Montgomery apparently said that same thing at about the same time.
In The Wrong War Why We Lost In Vietnam author Jeffrey Record noted that:
“Among other things, it violated an established strategic injunction against committing U.S. military power to a large-scale land war on the mainland of Asia. Since World War II, U.S. military leaders, including Omar Bradley, Douglas MacArthur, and Matthew Ridgway, had cautioned against ground combat involvement in wars on the Asian mainland, where, it was felt, U.S. naval and air power's effectiveness would be diluted, and where Asian foes could exploit their great superiority in manpower and bog the United States down in a protracted conflict. This strategically sound aversion underpinned the Truman administration's refusal to commit U.S. ground forces on behalf of the Nationalist Chinese government in the latter half of the 1940s as well as its opposition to MacArthur's pleas in 1951 to widen the Korean War. I t also played a significant role in the Eisenhower administration's refusal in 1954 to intervene on behalf of beleaguered French forces in Indochina.”
So the idea was well established and given the population dynamics in Asia, it basically common sense. At some point along the way, common sense was abandoned.
At the risk of stretching the point, one could argue that the experience of Alexander the Great, despite his many victories, was the first to pay the price for embarking on an Asian land war.
Even if some military force summoned the tremendous power and projection necessary to defeat land armies in Asia, the task of sustaining that control afterword would be overwhelming.