Why was a treaty between the native Americans and the US needed?

Treaty was needed to serve and satisfy a fundamental need of States to regulate by consent issues of common concern and thus to bring stability into their mutual relations between native Americans and US.

Explanation:

Treaties form the basis of most parts of modern international law. Like International environmental agreements are important because they enable countries to work together to deal with vital environmental issues which are trans boundary or global in nature for e.g. air pollution, climate change, protection of the ozone layer, and ocean pollution.

The federal government in many treaties agreed to guarantee education, health facilities, housing, and other services to native Americans. The United States also agreed to manage and protect inhabitant's resources, such as lands and timber.

i believe the answer is:

-   william jennings bryan is a democrat while mckinley was a republican

at that time, the segment of population that choose for democratic party were the voters with low economic background and vice versa

- william jennings has support of populists and wants to have inflation to farmers while mckinley has support of bankers and businessmen , doesn't want inflation

the fixed value of gold make the large business able to stack up their gold without   being worried that it would devaluated.

- william jennings supported the silver standard while mckinley supported the gold standard

according to jenning, using other metal beside gold could the poor people to have more purchasing power and them advance in the society.

sorry i cant