Catherine the Great's offer of troops to Britain during the Revolutionary War is taken up, and cossacks crush the American revolution. The habit of hiring Russian mercenaries in times of crises sticks.
During the 1860's, the Dominion of Texas is in crisis as its settlers fight the Comanches, but most of its fighting men are either in rebellion against the Crown due to the recent abolishment of slavery or fighting for the crown, but against the more eastern slave powers like Georgia, Alabama and the Cherokee Nation.
Once again Britain turns to Russia for help, but the Russian empire has found that Cossacks who fight in the Americas tend to stay in the Americas, and this emigration is depleting their troops. So, they offer the Tatar peoples a deal: fight in the Americas, and be granted land back that was previously taken by Russian settlers. And so the Tatars find themselves shipped to Texas, to fight another horse people on unfamiliar land.