History.com: Why Isn't Puerto Rico a State?

Located about a thousand miles southeast of Florida, Puerto Rico is a Caribbean archipelago with a complex colonial history and political status. As a territory of the United States, Puerto Rico's 3.2 million residents are U.S. citizens. However, while subject to U.S. federal laws, island--based Puerto Ricans can't vote in presidential elections and lack voting representation in Congress. As a U.S. territory, it is neither a state nor an independent country.