Some possible elements coming to mind for the idea described in my last post:
* Marx travels to the U.S. in late 1850s, to both write for the Tribune and study the possibility of revolution in the country given the looming Civil War.
* The Panic of 1857 occurs not long after Marx's arrival, piling on financial demands that force him to postpone returning to Europe, and to stay with the Tribune even after Charles Dana leaves the paper and Greeley shifts its editorial policy away from abolition (though he eventually begins to write for the Liberator under a pseudonym, to salve his conscience). Travels over much of the North and South during this period, and (maybe?) makes contacts throughout the German immigrant community (Examples: Francis Lieber, Carl Schurz, the Salomon brothers, Franz Sigel, the Turners/Turnverein).
* Traveling to the West on the eve of the war (to examine exactly how/if the frontier dissipates social unrest in America), Marx is stranded among the "Forty-Eighter" German communities in central Texas, which are soon targeted by the CSA given their Unionist sympathies.
* When Confederate troops enter the region in summer 1862 to arrest and/or execute Unionists, Marx joins a group of Union Loyal League refugees under Fritz Tegener (or Jacob Kuechler?). Their conversations eventually persuade the group to take a stand in the heavily German "Hill Country" (rather than flee to Mexico and then Union-held New Orleans, as in OTL) so as to rally anti-CSA citizens and form a Unionist enclave/state within CSA Texas.
* The Confederates eventually isolate and attack the group in the Hill Country, leading to a different version of the
Nueces Massacre, which Marx barely survives and escapes. The outrage from this attack spurs greater Unionist German resistance in Texas than in OTL, with Marx pushed into a military/political leadership role.
* End of the war finds Marx as de facto ruler or ideologue of the "Hill Country", based in New Braunfels (or San Antonio?) and governing with strong socialist leanings tailored to the rural nature of the region (??). Approached by Union officials regarding re-integration of the "commune", Marx is ambivalent...