Not in combat, not in warfare. North Vietnam did break the treaties and invade, and conquer the South, almost 2 years after we left.
That is where our Viets here came from.
Although we won in the field, we ultimately lost the war as our resolve failed and we did not support South Viet Nam as our promises and our interests required. Our allies turned refugee tend to be both socially conservative and ideological hostile to the Left. They are also willing to work and fight to defend their new country and its principles — which, in a flip way, was my point.