How was the U. S. involvement in these Cold War conflicts different than full scale invasions in wars like WWII?

The main difference between the involvement of the United States in the Cold War and the other wars in which it participated is that, in the Cold War, the United States did not directly attack its main adversary (the Soviet Union), but rather It did so indirectly, both through proxy wars (using third countries for it) and through economic and strategic policies clearly damaging to Soviet interests. Thus, the United States financed anti-communist movements in various countries of the world, such as military dictatorships in Latin America, placed dissuasive missiles in Turkey, became involved in the Korean and Vietnam Wars, etc. But never in the entire process of the Cold War did it attack the Soviet Union, which would have triggered a nuclear war of disastrous proportions.

Instead, in all its other warlike participations, the United States participated directly in military actions against its adversaries.

the event that was most responsible for ending the great depression is world war 2.