Korean War: won, South Korea was transformed into an american colony a la Japan, and is now used as a platform to counter China in the east as well as trading partner and military base.
Vietnam: countered Soviet expansionism and prevented Vietnam from becoming a communist regional superpower, Vietnam has not done much besides be a trading partner for the US since.
Grenada: won
Gulf wars: overwhelming victories. Destabilized the middle east, provided an opportunity for american megacorps to heavily profit and exert massive influence. Led to Arab spring which further destabilized the middle east. The middle east is essentially no longer in the picture in the game of global hegemony, and in large part has to rely on American refineries and american corporations to handle oil extraction.
Afghanistan: success, stimulated the American economy, very successful unemployment program (provided jobs for America's high school dropouts for 20 years), justified further weapons development plans, allowed america to build tons of bases to help counter China's Silk Road initiative by destabilizing the region.
Syria: mostly a failure at this point. The hope was to break Syria and build the Qatar gas pipeline to hurt Russia's hegemony on european energy supplies. Looks like that is a lost cause at this point, but of all the wars America has recently waged, this one is probably the most justifiable.
The world is no longer about winning wars and conquering territory. It's about destabilizing rising threats to your power. It's about toppling dictators and installing democracies, which are much easier to bribe. It's about countering your enemies/competitors (Russia, china, the middle east) initiatives and causing chaos in their neighborhood.