It could be because most Americans have ancestors who immigrated from Europe and thus identify with Europeans more readily. It could be because many Americans have been tourists in European countries and so it is more personal to them. It could be because more Americans have cultural similarities with Europeans. It could be because we have treaty obligations to countries surrounding Ukraine. It could be because, in the cases of Rwanda, Syria, and Libya, they were fighting civil wars. (And in the case of Iraq we were the aggressor and maybe the U.S. should have been sanctioned for its invasion.) It could be because we are, rightly, horrified of one country simply rolling over another. It could be because, as the 1619 Project highlighted, we have some deep racism in our country. I suspect it is a combination of all of the above.