The Missouri Compromise, passed in 1820, was an agreement between the pro-slavery and anti-slavery factions in the United States Congress. It concerned the regulation of slavery in the western territories. It admitted Missouri as a slave state to please the South. It admitted Maine as a free state to please the North. It kept the balance of power in the United States Senate between the free states and slave states. The plan also called for slavery to be banned from the Louisiana Territory north of the parallel 36 degrees 30' north (also known as the Missouri Compromise Line), except within the boundaries of the proposed state of Missouri. It was a temporary measure that reduced the conflict over slavery. But there was continued resentment between North and South. The South resented Congress interfering with slavery. The North resented having to compromise on the moral issues of slavery. Both sides wanted the political power necessary for their issue to win. In his book "Negro President: Jefferson and the Slave Power", historian Garry Wills wrote, “the South was not demanding slave representation to achieve a near-parity at the moment, but as a way of achieving majority control in the immediately foreseeable future.”