The US owns a bunch of Caribbean "territories" that they still won't make into US states. Their citizens are US citizens, but can't vote.

EDIT: The current US itself was carved out of territories owned by Mexico, France, and England (which took them from Native American tribes). Back in the day, we conquered and stole a bunch of land, both from natives and from other invading countries.

But we've been more interested in foreign politics since WWII and less about expanding our own land. Besides, why own a bunch of foreign soil when we can just set up outposts around the globe and have a military frontline anywhere? I served in the US military and we have so many bases scattered around every region of the globe. We can literally involve ourselves in any global conflict we want to within a day or two. Meanwhile, our actual homeland is isolated on the other side of the planet, where it's difficult for foreign invaders to touch us.