Thirteen British colonies became states in 1776, and each of those states ratified the US Constitution after its creation in 1787.

The Constitution assigned to Congress responsibility for organizing new states. Congress created a precedent with the Northwest Ordinance of 1787, requiring potential states to have a population of 60,000 people. Homesteading opportunities and mining attracted many settlers to the territories that gained statehood first. The new states had been territories purchased from other countries or won through warfare.

As travel to the West became more efficient and trade became more profitable, migrants moved to territories in the southwest and mountain west regions, and they became new states. The mainland United States was complete after Arizona’s admission in 1912. In 1959, Alaska and Hawai‘i became states. Alaska had been purchased from Russia. Hawai‘i had been seized from native Hawaiians.