Why did the United States military first become involved in Vietnam

To stop the spread of Communism.

Explanation:

During the Cold War, the U.S.S.R. and the U.S. were fighting to decide if Capitalism or Communism would be the dominant market type.  The U.S. entered Vietnam to help fight out the Russians who were trying to establish a Communist government there.

the answer is use of support  

the foundation of greek city-states: following the fall of the mycenaean civilization in the 10th century bc, the area surrounding the empire went through its own mini dark ages. answer and explanation