Why were we in Vietnam?

I was in VN from 7-69 to 7-70. I was in the infantry (11 Bravo), Alpha 2/8th 1st Cav. 

One day we came to a small village and we were to check it out for bad guys. I looked in a grass hut and all I saw was nothing, nothing at all, just a bare floor and a mat to sleep on. No furniture, not a table or a chair, nothing but a poor old man sitting on his hunches.

I looked at him and asked my self, "I wonder if he gave a shit if he had a communist, socialist, or even democratic form of government" the answer was clear to me. Hell no! He just wanted to be left alone to farm and feed himself and his family.