We shoudln't invade ANY country without a darned good reason. Invading Afghanistan (Islamic) made sense--getting rid of the Taliban and al-Quaeda's infrastructure. Invading Grenada (marxist-leninist)made sense--eliminating a communist outpost on our doorstep. Attacking (we didn't really invade) Serbia was cowardly and pointless; it was no threat to the USA or its interests AT ALL. A waste of treasure and (mostly Yugoslav) lives.
Okay - I was just clarifying.
What degree of threat? Long-term strategic or short-term imminent would be required? I can safely put Afghanistan in short-term imminent threat and maybe Grenada in long-term (although not sure how much since Cuba hasn't brought about a land invasion yet). Not being offensive - just clarifying your statement.
I believe Kosovo was a threat to the stability of NATO and our surrounding allies. Was it a threat to the US itself? No.