The USA government by constitutional procedure protected slavery.
Fact.
Wrong
States that outlawed slavery.
Vermont - 1777
Pennsylvania - 1780 - Pennsylvania's law passed in 1780 was for the "gradual abolishment of slavery" to take place over a period of 20 years.
Massachusetts - 1780
New Hampshire - 1783
Connecticut - 1784
Rhode Island - 1784
New York - 1799
New Jersey - 1804
Northwest Ordinance
Art. 6. There shall be neither slavery nor involuntary servitude in the said territory, otherwise than in the punishment of crimes whereof the party shall have been duly convicted: Provided, always, That any person escaping into the same, from whom labor or service is lawfully claimed in any one of the original States, such fugitive may be lawfully reclaimed and conveyed to the person claiming his or her labor or service as aforesaid.