The 36th Parallel South is a circle of latitude that is 36 degrees south of the Earth's equatorial plane. It runs through several countries, including parts of Australia, New Zealand, and South Africa. This parallel is significant in geography and climate studies, as it often marks the boundary between different climate zones. In the United States, the 36th Parallel South is notable for its historical context, as it was used as a boundary in the Missouri Compromise of 1820. This compromise aimed to maintain a balance between free and slave states, with the parallel serving as a dividing line for future states in the west.