We entered WWI late in the game and "only" suffered 53k combat deaths. WWI was huge for the major combatants of France, Germany, Russia, and Austria-Hungary, each of whom lost over a million in combat, plus the British empire which lost just under a million between England and all her subjects. To put it in context, more Canadians died in combat in WWI than Americans, and Canada at the time was much less populated than the US, even more so than today. Source: https://en.wikipedia.org/wiki/World_War_I_casualties

So, yeah, we don't tend to think of WWI as much as being one of the major wars we were involved in. The major wars we tend to think about in our cultural consciousness are the Revolutionary War, Civil War, WWII, Vietnam War, and then because of the recency bias, the "global war on terror" in Iraq/Afghanistan. WWI is covered in history classes of course, but primarily from the western front perspective, which the US didn't get involved in until the war was almost won.

The US reacted to the end of the first world war by retreating from global affairs. They didn't even join the league of nations their president was instrumental in creating. WWI was terrible, but it simply did not result in the drastic societal changes that WWII caused.

WWII was the start of a new world order with the USA at the forefront.