After the civil war ,why did the federal government try to the african americans to the northern status?

I'm assuming by "status," you mean "states." If not, please correct me so I can correct my answer.

The federal government knew that African-Americans would face backlash from Southern White males, so they wanted to prevent that from occurring at all.

I hope this answer helped you! If you have any further questions or concerns, feel free to ask! :)