Gadaffi was a nominal socialist who kicked the US military out, aligned himself with the Soviet Union, proposed pan-Arabist and pan-African alliances to exclude the west and was implicated in bombings of US targets, undermining US-allied causes overseas etc. And yes, he nationalized the oil industry early in his rule. Even if he briefly achieved some sort of rapprochement (mostly with the EU) when he'd run out of allies, he's pretty much the exemplar of how to piss off the US, and so them helping finish his regime off fits the pattern perfectly.