Why did the federal government stop protecting the rights of black Americans after 1877?

In all, with the Compromise of 1877, the Republican Party abandoned the last remnant of its support for equal rights for African Americans in the South. With the withdrawal of federal troops went any hope of reconstructing the South as a racially-egalitarian society after the end of slavery. As Henry Adams, a black Louisianan, lamented, “The whole South—every state in the South—had got into the hands of the very men that held us as slaves.”
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In the aftermath of the Compromise of 1877, a few African Americans in some areas of the South continued to vote and serve in government offices into the 1890s, but the Compromise of 1877 marked the effective end of the Republican Party’s active support of civil rights for black Americans. Southern states rapidly passed laws disenfranchising African Americans and implementing racial segregation.