Well enough to know that, had we not been integrally involved in WWI, two things likely wouldn't have happened: the rise of Nazism in Germany and the rise of Progressive collectivism in the United States, both of which contributed significantly to the onset of WWII.
There's also the oil embargo we placed on Japan. And playing sides with England against Germany without actively declaring war. But really, it was WWI that laid the ground work for what inevitably followed: WWII.
How well versed are you on WWI?