Like every single other country, the United States looks out for its own interests first. In addition to the wholesale slaughter of Native Americans, America also committed less-publicized but equally barbarous atrocities during occupation of Germany after World War II and upon the Iraqis during the Gulf War. I'm not even going to touch Vietnam or slavery...
However, before you get into a cynical funk about America's evil, just think of all the achievements this nation and its populace have achieved: scientific research, art, medicine, information technology, the spreading of democracy and the freedoms associated with it, unprecedented regard for peace and human rights, unprecedented wealth and economic production, military protection of dozens of other countries (including many on the list above) the destruction of Hitler and other tyrants, etc.
You can't really put a moral value on a country, but I'd say the achievements of the United States balance out the negatives. Every other country is just as "guilty."