The USA were in Viet Nam to prevent a massive communist block from overtaking SE Asia. They were merely moving into the vacuum created when France Britain Holland etc were kicked out of those countries.
So what? It means nothing to the USA. It will not impinge on your freedoms or your way of life will it?
And when SE Asia has become a no go zone for westerners, the effect spreads to the Pacific islands and possibly even to Australasia in one direction, to Burma, Pakistan and India in the other.
Your trade becomes blocked, your imported goods impossible to obtain, no market for your exports. But that will not effect your way of life or your freedoms will it?
Money? No it is not JUST about money. If you think you can exist without free trade then you have your head buried in something a bit more substantial than sand.
Outside your own country your civilians would not have the freedom to travel, to gain new ideas or to put forth friendship to those other countries to which you are now denied access.
Soldiers do not die for money - they die for you and to preserve your way of life.
Some idiot said that war was the last act of diplomacy or something similar (cant be bothered to look it up) but whoever said it was dead right. If you have no military, your diplomats are toothless.
And so is your country.
If you have no army then you had better learn to suck.