When empires fall it happens in stages, not all at once. The decline of the United States began on 11/23/63 with a coup against President Kennedy and has been slowly ongoing since. The Biden meat puppet is the last piece, unless DJT defies the odds again. Vote for him like our nation depends on it.
No, as a Southerner, I’d say when Lincoln compelled the Southern states to remain in a Union they no longer wanted a part in.
At the least, the Southern states that had been part of the original 13 colony USA—and signed into it—should have had standing to dissolve their ties to the union.
Then again, when Hoover tried to fix the economy with government solutions (but not enough to effect it) and then especially When Franklin Roosevelt stepped up government to replace the economy and usurp economic choice is where we went off track.
One can argue it’s been going downhill for longer than it has existed.
In that case, our fall began in November 1960 when the election was stolen from Richard Nixon in order to put a liberal coward into the White House.