Answer:
B. Economic development would get rid of the need for slavery.
Explanation:
The correct answer to this open question is the following.
I think the U.S. backed down on its enforcement of the Treaty once gold was discovered in the Black Hills because the United States federal government had already signed and formalized the Treaty of Laramie in 1868, in which the government recognized that region of Black Hills as a territory of the Sioux Native American Indian tribe.
Let's have in mind that although large gold deposits were found in 1875 in Deadwood Gulch, Black Hills territory and thousands of people went there to find fortune, the territory already belonged to the Lakotas and the Sioux.
In their competition for power, nations raced to colonize as many places as possible, since colonization meant an increase in raw materials, as well as usually an increase in labor force through exploited natives.
Under Article I, Section 8 of the Constitution, Congress has the power "to make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or any Department or Officer thereof".
