Shouldn't this be in "After 1900" or even "Chat"?
Nope. As I said in the OP, there is a thread about the actual news story in "Chat"; this is a challenge to get the same headline in an ATL with a POD before 1900, with the unstated (but not required) assumption that it's actual Russian Cossacks vs. actual Mexican/Spanish-American bandits. (For example, you could posit a Confederate mounted guerrilla group a la Mosby who took the name "Cossacks " to strike terror into Unionist hearts).
I put this up in "After 1900" as well. Say, bigger American support for the Whites in the Russian Revolution, with a band of Cossacks being evacuated to America and ending up settling in Texas because of their horsemanship.
Or a group of Cossack cavalry fighting for the Germans in WWII being shipped to the Western front after the Battle of Kursk, being captured, sent to America as POWs, then being allowed to stay by pleading their case to an anti-commie Texas Senator. They settle on the border and their descendants end up fighting drug and people smugglers. Can't you just picture Fox News eating up a pistol-packing anti-commie anti-immigrant beautiful blonde Russian-Texan on horseback?
As I understand it, threads concerning post-1900 events belong here if the POD is before 1900- though this headline could be either 19th or 20th/21st C.