After the Civil War, the Union survived because the focus was put on everyone being Americans! Northern or Southern, Black or White... we're all Americans! Some people still didnt like it, so we got the KKK, Jim Crow, etc... They were a minority, and kept getting smaller. But the Party that got their votes discovered they didnt have to pander just to Southern Whites. They started Pandering to EVERYONE THEY COULD! They figured out that Divide and Pander was their Strength! Poor vs Rich, Industry vs Farmers, Urban vs Rural, Black vs White, Men vs Women...
They encouraged Tribalization, and pit those tribes against the whole. They framed it as a moral issue.. "how dare you force the minority to conform, you Bully!" And so the Great Melting Pot became the Great Pile of Discordant Things. Differences were exaggerated, separation was encouraged, unity was called tyranny, assymalation was called genocide.
The Churche were infiltrated to stop teaching morality, and only offer platitudes. The Education System was overrun, so schools only taught sophistry. The Media Complex lost all sight of morality as one court ruled "you cant stop pornography".
And now, 150 years of relentless assault later, we are seeing the fruits of their labor. A House divided against itself cannot stand.