In 1818 Missouri became a state.
In 1820 an agreement called the Missouri Compromise.
Maine became a state in 1820. Missouri became a state in 1821. For the next 15 years no states entered the Union. From 1836 to 1850 six states were admitted:Arkansas1836
slave
Michigan 1837 free
Florida 1845 slave
Texas 1845 slave
Iowa 1846 free
Wisconsin 1848 free