The purpose of the Act of 1871 was to fully enslave the American people by the international bankers. It was done by stealth, behind closed doors. The American people were not told about it in an honest and public manner.
The Act of 1871 as you are calling it is not its full name. It’s action name is the District of Columbia Organic Act of 1871. It established a new, unified government for Washington, D.C. It “incorporated” that city, a common legal term by which areas are organized for governance by a single entity. In this case, two cities and a county were merged into the District of Columbia. It made no changes in the nation as a whole.
A PDF pith text of the legislation