Statehood Process and Political Status of U.S. Territories: Brief Policy Background [Updated March 19, 2021] [open pdf - 460KB]
From the Document: "Proposals to admit new states to the union are as old as the republic. An expanded United States was contemplated at least as early as 1787, with enactment of the Northwest Ordinance, which addressed territorial expansion, even before the first states ratified the U.S. Constitution later the same year. Vermont joined the union in 1791, the first new state beyond the 13 original colonies. Arizona and New Mexico completed the contiguous United States in 1912. Alaska and Hawaii became the 49th and 50th states respectively in 1959. Would-be states have relied on different methods to join the union, and there is no single process for doing so. This In Focus provides brief background about the statehood process generally, and about how it might affect congressional consideration of proposed statehood for U.S. territories."
CRS In Focus, IF11792
Congressional Research Service: https://crsreports.congress.gov/