There are a number of possible outcomes.
Explanation:
Firstly there are outcomes for the countries experiencing US involvement, and secondly there are outcomes for the US. In many instances the US is the beneficiary at the expense of the countries. This has been true in Central and South America for the last 200 years as successive American power elites have supported brutal regimes and dictatorships to secure economic interests. Examples would be Cuba under Batista where the Mafia controlled the hotels, casinos, and prostitution, the overthrow of the democratically elected Allende regime in Chile and the support for right wing death squads in El Salvador in the 70's. Â The same can be applies throughout the globe including, Africa, Asia and The Middle East.
The US became involved in the Vietnam war for a number of reasons. The decolonisation process after WW2 led to the withdrawal of European powers and the emergence of new countries. In French Indo China the French were defeated at Dien Bien Phu in 1954, and Vietnam was split in 2 with Cambodia and Laos being declared neutral.
These developments in the context of the Cold War led to the Soviet Union and USA competing for influence and control. North Vietnam was supported by the Soviet Union and the South by the USA.
The situation in the south deteriorated during the 50's and early 60's as the corrupt American supported Diem regime refused to hold reunification elections.
In 1963 Diem and his brother were assassinated by a CIA backed coup and the military took over. Soon after Kennedy was assassinated in Dallas and military involvement rapidly escalated after Johnson took over, even though he thought, in private, it was a lost cause.
The concept of the Domino Theory is also applicable, namely you have to draw a line to stop communism or a whole line of countries will fall.
There is also the role of the Mafia and access to The Golden Triangle of heroin production which was shipped back to the US in the bodies of dead GI's.
