The missouri compromise angered because congress had allowed slavery to expand into another state. henry clay white southerners northerners thomas jefferson

The correct answer is Northerners.

The Missouri Compromise allowed the state of Missouri to enter the US as a slave state. Along with this, it allowed Maine to become a free state and established the 36'30 line as a means to determine where slavery will exist in terms of adding new territories to the US.

Northerners were angry at this because any new slave state added would result in more pro slavery politicians in both branches of Congress, including the House of Representatives and the Senate.

The correct answer is Northerners. 
The Missouri Compromise allowed the state of Missouri to enter the US as a slave state and Maine as a free state. This angered Northerners as they felt like Congress had allowed slavery to spread to another state. 

Not sure this is a hard one huh