My impression was that in all instances you mentioned we intervened only after other foreign powers did so. Am I wrong?
There’s a lot of specifics if you want to consider us after the other powers. However, in the Civil War portion of Vietnam (Vietnamese vs. Vietnamese) we were the lead to getting involved in Vietnam. There were revolts against the French in the late 1940s and up to 1954 when the French withdrew, but this was not a civil war because it was not Vietnamese killing each other, for the most part.