Which of the following factors best explains the territorial expansion of slavery in the middle of the nineteenth century?

The expansion of US territories

Explanation:

Jefferson's acquisition of the Louisiana territories in 1803 doubled the size of the US coupled with the victory in the Mexican-American War extending the U.S territories to the Pacific which further tripled its area. This expansion invariably led to the spread of slavery.

The Mexican american war incorporated extensive new lands into the United States.

were at first enthusiastic in support of the revolution. however, over time divisions of opinion became apparent between federalists and anti-federalists

i would say the executive branch is because the executive branch is in charge of enforcing the laws and judicial branch is in charge of enforcing but the executive branch is most responsible for it all so i would have to say the executive branch.