A great and continuing weakness of the United States Army fighting in Asia, T. R. Fehrenbach argues (in This Kind of War), was its tactical and psychological dependence on continuous battle lines, such as had been known in Europe:
In Asia, terrain and Communist tactics made such lines rare — Communist armies tended to flow like the sea, washing around strong points, breaking through places where the dams were weak. The “human sea” analogy picked up and headlined by the press was very real — except that the press always gave a misleading indication of the numbers of enemy involved. Relatively small numbers of enemy flowed around the high ground held by American troops, went behind them, and interdicted their supply roads.
Road-bound, the American commanders became understandably nervous. Invariably, both men and leaders began to think of retreat, falling back to form a new line. This was in many respects a frame of mind. The North Korean forces in the American rear were small, ill supplied, and in effect often cut off from contact with their own bases.
Able to live on three rice balls a day, capable of carrying guns and ammunition over the steepest slopes on foot, this isolation bothered the Communists not at all.
It drove the Americans, hating isolated action, dependent upon wheels, to desperation. Ironically, the Indian-fighting army of seventy-five years earlier would have understood the new form of warfare perfectly. On the plains and mountains of the American West, the United States Army had once learned everything there was to learn about hit-and-run tactics and guerrilla warfare. It had learned to ride hard and march hard, live light, and to operate in isolated columns, giving the enemy no rest.
But even hard lessons can be soon forgotten.
The Chinese were practicing blitzkrieg on foot in the mountains. Envelopment is the core tactic. On the plains of Russia it was done with tanks and mechanized infantry. Apparently MacArthur learned nothing from WW II.
On this, I’ll cut them slack. 75 years is time enough to forget. Everyone who lived through the frontier wars would have been dead by then.