Look at a map of the United States. Maine sits at the very top of the east coast, bordering only one other state -- New Hampshire. But Maine was not always its own state. For over thirty years, it was the northern part of Massachusetts, even though it was not even connected to it. The people living in Maine wanted to govern themselves. On March 15, 1820, Maine officially became the 23rd state. There was a catch, though. At the time, the country was trying to keep a balance between free states and slave states. Congress said Maine could only join as a free state if Missouri joined as a slave state at the same time. This deal was called the Missouri Compromise. Maine's geography is shaped by the Atlantic Ocean. It has over 3,000 miles of jagged coastline, more than California. Cold ocean currents bring thick fog and icy winters. The state is covered in dense forests, and its nickname is the Pine Tree State. Maine's most famous industry is lobster fishing. The cold, rocky ocean floor is perfect for lobsters, and Maine produces more lobsters than any other state.