Originally settled in 1607 by the Plymouth Company, the coastal areas of western Maine first became the Province of Maine in 1622 land patent. Eastern Maine north of the Kennebec River was more sparsely settled and was known in the 17th century as the Territory of Sagadahock. The province within its current boundaries became part of the Massachusetts Bay Colony in 1652, and was part of the State of Massachusetts when the United States was formed. Because it was physically separated from the rest of Massachusetts and was growing in population at a rapid rate, it became the 23rd state along with Missouri on March 15, 1820. This has become known as the Missouri Compromise because admitting both states into the union kept the balance between slave and free states. Maine's original capital was Portland until 1832, when it was moved to the more geographically central city of Augusta.