Answer:
The American territorial expansion in the first half of the 19th century allowed for the expansion of slavery, too.
In the new territories purchased, annexed or taken by war in different times, new states were created and admitted to the Union, and some of them were admitted into the Union as slave states, some became free states. Anyway, the issue of slavery was a core issue in domestic politics.
For example, Louisiana and Arkansas turned into slave states (Louisiana Purchase). Texas (annexation) was a slave state, too. California, won in the war with Mexico, joined the Union was a free state.
From 1812 through 1850s, hard political bargaining and legal mutual concessions in Congress took place in order to preserve a delicate balance between slavery and free states.
Explanation:
