Actually, we started getting actively involved in Vietnam during Truman's reign by supplying support to the Frogs, er French.  However, you can go all the way back to Woodrow Wilson to see our political involvement.

I wasn't going to post in this thread because of the left and right pointing fingers at each other.  These wars we've been involved in are very complex and intertwined.  The one thing that rings true is BOTH the left and the right participate in inflaming situation internationally that result in us thinking our active involvement is necessary, when in reality it isn't.

America and Americans love violence and their wars.  That's for sure.