Recent events in the US have prompted anti-racism activists, and the general public at large, to highlight America’s role in combatting right-wing governments, particularly those it fought during WWII. Indeed, America exclusively fought against nationalistic powers across the globe from 1941-1945, reorganizing Germany, Italy, and Japan after the war. So the sentiment “America fought the war to defeat Nazis” or Fascism appears self-evident. It is an exxageration, perhaps even ‘fake news,’ because of its inaccuracy, though. That is not to downgrade the fact that the US opposed Nazi-Fascist aggression and aspects of Nazism. Here is the truth about Americas relationship with right-wing extremism during WWII but also before and after.
The key event of course is Pearl Harbour. It left the US with little choice but to declare war on Japan, a country it had already sanctioned. However, the US did not declare war on Germany until December 11th, 1941. That was after Germany declared war on the US. Before December 1941, the US had adopted a nuanced stance regarding the Nazis. Relations had cooled after the 1938 Kristallnacht. Roosevelt used his presidential prerogative to support the Allied cause. A clear moral distinction was made between the Allies and the Nazis, but also between the Allies and the Soviet Union (the USSR had attacked several countries during WWII), although the US slightly favoured the USSR (there were strong pro-Soviet sympathies in the cabinet and in the bureaucracy). Public opinion in the US favoured neutrality and was not ill-disposed to Hitler in the main. It must not be forgotten that the key US foreign policy was isolationism, as opposed to any ideological opposition to totalitarianism. The proof is that the US forged a long-lasting alliance with Fascist Spain because Franco respected international borders and managed his public perception in a way which made friendship viable.
Its also disingeneous to say that America existed in a completely different moral universe to Fascist/Nazis. During WWII, and for decades before and after, Jim Crow laws segregated whites and blacks across much of the US. Immigration laws were passed, notably in 1924. Their intention was to protect white majoritarianism and they also had an element of anti-Judaism paranoia. Furthermore, the extermination of the Indian natives offers clear evidence of American exceptionalism. Lastly, eugenics was popular as in Nazi Germany, having official backing in many quarters.
US policy after the war showed the true face of American policy towards right-wing governments. Fascist and tyrannical governments were supported from Chile to Vietnam to the Phillipines, although some were more acceptable than others. This was to counter Communist expansion, proving the primary US preoccupation was with international order.
In conclusion, America fought WWII out of necessity, not to defeat right-wing extremism. The US entered the war because it had war declared upon itself. It was prepared to work with Fascist regimes who respected international norms and overtly demonstrated this support after the ink dried on surrender documents in 1945.