South American countries fell into dictatorships becuase they had the same conditions which supported dictators in Europe. Economic instability led to loss of faith in democractic institution. The military was more efficient than a legislature. However, one thing unique to Latin American states was the type of involvement by foreign governments, especially the United States, in their internal affairs. The US involvement in Latin American countries' internal affairs stemmed from the fear of increasing influence of Soviet Union during the Cold War.
The United States had a unique experience in that it had ample time and space to tackle the challenges it faced including a bloody civil war, expanding across the continent and giving equality to Blacks. There was no direct intervention by foriegn powers in American affairs. Moreover the founding father of United States had set up the tradition of a strong legislature. George Washington, the first American president, voluntarily gave up his military commission back to Congress after the Revolutionary War was over. He also left the Presidential office after two terms thereby creating a strong tradition.
