Country has divisive civil issues. US backs the side wanting democracy and pro-Western ties. Communist Asian country backs the side wanting socialist and pro-Eastern ties. Both sides appeal to their bigger allies for help. Both allies send aid, both military and otherwise. A civil war ignites. Suddenly, the two larger allies are fighting a proxy war inside that country.
Sound familiar? I don't think we'll see another Korea, Vietnam, or Afghanistan (circa 1980s) anytime soon, especially in Europe.