The discovery of what resource, in 1874, in the Black Hills of South Dakota caused the U. S. government to break their treaty with the Dakota Sioux

Gold.

Explanation:

A series of clashes between the Northern Cheyenne, Lakota Sioux and the United States that took place in the years between 1876 and 1877 for the occupation of the Black Hills was known as the Great Sioux War. The discovery of the gold in the Black Hills and the U.S government's desire to establish its control over the Black Hills were the main causes of the war.

representative government

tenochtitlan (also spelled tenochtitlán), located on an island near the western shore of lake texcoco in central mexico, was the capital city and religious centre of the aztec civilization. the traditional founding date of the city was 1345 ce and it remained the most important aztec centre until its destruction at the hands of the conquering spanish led by hernán cortés in 1521 ce, which led to the final collapse of the aztec empire.