> If the US wanted to, and if it did it correctly, it could easily conquer most countries.

It could possibly conquer many countries by largely destroying them as was done to Germany and Japan, but since the US is a democracy and a sizable portion of its people have morals and aren't sociopaths, it's politically impossible to fight a war this way in the modern era without some kind of extreme provocation. Even immediately after 9/11, I think most Americans would not have signed on to a campaign of total war in Afghanistan with multiple millions dead.

And even back when America did pretty well take the gloves off, doing nearly everything it could short of nuclear weapons in Korea and Vietnam, it still couldn't win. So I don't think it's a foregone conclusion that any decent-sized country could be conquered easily even if the 'will' was there.

> Even immediately after 9/11, I think most Americans would not have signed on to a campaign of total war in Afghanistan with multiple millions dead.

This falls clearly under 'not wanting to'.