 Formal secession and formation of the state of Maine as the 23rd state occurred on March 15, 1820, as part of the Missouri Compromise, which geographically limited the spread of slavery and enabled the admission to statehood of Missouri the following year, keeping a balance between slave and free states.Maine's original state capital was Portland, Maine's largest city, until it was moved to the more central Augusta in 1832.The principal office of the Maine Supreme Judicial Court remains in Portland.