1861: Abraham Lincoln runs for the Presidency on a platform opposed to the expansion of slavery in the western territories. Needless to say the South doesn’t vote for him (who’s gonna grow all that cotton and tobacco for them?)
Instead, just weeks into Lincoln’s presidency, the Civil War begins as the South tries to secede, mostly because their entire economy relies on enslaving others to function.
Lincoln takes it all the way, signing the Emancipation Proclamation in 1863, which frees everyone who’s been enslaved (though it takes everyone a while to get word). The Civil War utterly bankrupts the South.
But before he does that, he does everything he can to make sure that the westward expansion is comprised of people sympathetic to the Union cause. He signs four bills and a proclamation into law. Perhaps the two most influential are the Homestead Act (when all is said and done, 30 states and 270 million acres are “opened to settlement and agriculture”) and the Pacific Railway Act, which creates the great Transcontinental Railroad (and which he makes sure runs along a northern route).
With the South in ruins, the Western cowboy kind of picks up the slack, creating what we’ll eventually call “cowboy individualism.” We’ll paint a nice romantic picture around this guy single-handedly defending “his” land against “savages” or anyone else who wants to tell him what to do with it. Southerners will really vibe with this. Country and western. But also, an ironic twist considering…
Eventually we get all the way to the Pacific Ocean. When we run out of lands to take, we move to imperialism via markets instead.