Everyone knows that America is 50 states and...some other stuff. Scattered shards in the Pacific and the Caribbean, the not-quite states--American Samoa, Guam, Puerto Rico, the Northern Mariana Islands, and the U.S. Virgin Islands--and their 4 million people are often forgotten, even by most Americans. But they're filled with American flags, U.S. post offices, and Little League baseball games. How did these territories come to be part of the United...