After Independence the 13 colonies had to find a way to allow new states to become part of the United States. Before the end of the 18th century three new states joined, Vermont, Kentucky, and Tennessee.
The Ordinance of 1787 was a ban on slavery in the North-West territories. Each slave state that became a part of the United States a free state was also added. They did this to keep the balance between free and slave states. Ohio, a free state, was admitted in 1803 and in 1812 Louisiana was admitted as a slave state.
There was a lot of debate on slavery in America at this time. Cotton was a new product in the south, this made southern states want slavery more. The following free states were admitted next, Indiana and Illinois. Mississippi and Alabama were admitted at the same time as slave states. This kept free and slave states equal. Missouri wanted to join the United States as a slave state but this created problems. To solve the problem Maine, a free state, was created and a line was made marking free and slave states in the future. This was called the Missouri Compromise. In 1836 and 1837 Michigan, a free state, and Arkansas, a slave state, were admitted. Next were Florida and Texas, both slave states, in 1845 and Iowa and Wisconsin, free states, in 1846 and 1848.
After this, the western states were not good for farming and in 1850 California wanted to join the United States as a free state. To solve this problem, in 1854 the Kansas-Nebraska Agreement was signed. This allowed each state to decide if it wanted to be a free or slave state. In 1858 and 1859 Minnesota and Oregon joined the United States. Now there were more free states than slave states, causing many problems. In 1861 Kansas, a free state, became a state and Abraham Lincoln was elected President. These events caused the southern states to get very angry and seceded, causing the Civil War.