"Direct every military operation toward a clearly defined, decisive, and attainable objective. The ultimate military purpose of war is the destruction of the enemy's ability to fight and will to fight. "
http://fas.org/irp/doddir/army/fm3-0.pdf
US Army Field Manual FM 3–0
To win a war, it means you have hit your objectives going into the war. I wouold say that the objective for each US war was to destroy the infrastructure of the countries attacked by them, reduce the population, promote terrorist reactions, take over their economy and and gift the central banking function private bankers, spend trillions of tax payers money whilst cities in the US go bankrupt....etc so therefore the US has won every war decisively they have been a part of. If you base it though upon the stated by the puppet in chief the reasons for war and the objectives (peace , stability, democracy blah blah) then they have failed each and every time.