Sadly, WW2 is somewhat of an exception to most US wars since the Civil War, the other somewhat justifiable wars were the Korean War, the First Gulf War and the Yugoslavian intervention.
Unfortunately shit like Vietnam, Nicaragua, the CIA in Guatemala, Gulf War 2, the Afghan Occupation tend to overshadow the few "good wars".
It is also somewhat true that the US bares some political responsibility for WW2, tho in a somewhat convoluted way. There are 2 arguable things to be taken into account.
1, The US forced Japan out of its centuries long isolation at the barrel of a gun (many Naval Guns), thus shaping Japanese perception of their role in the world. Japan seen itself in a position were it would either end up being ruled by foreign powers or becoming a major maritime colonial empire. It is an interesting academic exercise to ask, had Japan been allowed to maintain its isolationist stance, would have it ended up becoming a colony, or something akin to Nepal, a largely independent, but somewhat isolated and backwards nation? If so, what would have its role been in WW2?
2, The US acquiesced to the Treaty of Versailles and to the latter Treaty of Trianon which neither pacified or reconciled the Central Powers, nor Italy who was shafted by its Western Allies after the First World War, directly leading to the political and economic instability that permitted the rise of Fascists and National Socialists who made the continuation of the First World War their priority.
Had Woodrow Wilson stuck to his guns and his "Fourteen Points" the entire fucking debacle of WW2 could have been easily avoided. Tho admittedly the US didn't quite wield the amount of international influence at the time as t did at the end of WW2.