Madison's maternal grandfather was a prominent planter and tobacco merchant. In the early 1760s, the Madison family moved into a newly built house, which they named Montpelier. Born into a prominent Virginia planter family, Madison served as a member of the Virginia House of Delegates and the Continental Congress during and after the American Revolutionary War. He became dissatisfied with the weak national government established by the Articles of Confederation and helped organize the Constitutional Convention, which produced a new constitution to supplant the Articles of Confederation. (The domestic trade in slaves was expressly permitted by the constitution.) He also proposed that apportionment in the United States Senate be allocated by the sum of each state's free population and slave population, eventually leading to the adoption of the Three-Fifths Compromise. Madison supported the extension of slavery into the West during the Missouri crisis of 1819–1821.