Before the invention of barbed wire, cattle assumed a quasi-feral status that relied on brands--traditionally large and more centrally located on the animals than the rump--to tell whose were whose.
Texas was a huge slave state, hence the decision to be the seventh state to secede. If one pays close attention to Torget's book Seeds of Empire, Texas seceding from Mexico and expanding the southern chattel slavery tied to cash crops (cotton, rice, sugar to a lesser extent) model of development (even José Antonio Navarro favored it, hence his siding with Anglo-Texians), formed the model for southern slave states seceding from the United States.
Don't forget that during the U.S. Civil War, a Tamaulipas caudillo Juan Nepomuceno Cortina was literally giving patentes de corso/ or letters of marque to ruffians, rustlers, and brigands to go north of the Río Grande/ Río Bravo del Norte, and drive cattle south across the Guadalupe-Hidalgo-mandated middle channel of the river as the national boundary between Texas and Mexico. No less a personage than Robert E. Lee had been through the line of forts along the river in 1860 to talk to Mexican officials about suppressing such rustling and brigandage... With the U.S. Civil War, all bets were off.
There was an ongoing Civil War and international conflict in Mexico. Recall that with the U.S. Civil War going on, the Monroe Doctrine calling for European Powers to adopt "hands off!" approaches to colonialism in Latin America--kindred American Republics--was mooted. So Spain tried to resume control of the Dominican Republic--failed--and Guatemala adopted the red and yellow of Spain to add to its blue and white Central American flag... But France of Napoleon III assailed Mexico and tried to install Maximilian von Hapsburg, the Austrian Archduke, and his Belgian princess Carlota as the Emperor and Empress of Mexico in the second Mexican Empire. Coservatieves and pro-clerical elements rallied to the Imperial throne. Benito Juárez and the pro-capitalist, pro-Republican Liberals rallied against him... And obtained recognition and even supplies from Abraham Lincoln, and later Johnson.
Meanwhile, the Shoshonean Nermernuh/ Comanche did not hesitate. They raided and burned and pillaged, and the pale of settlement receded eastward. Small wonder that Texans were allowed to form TST or Texas State Troops to stave off the depredations from the Comanche and Mexicans. In the meantime, huge sums of money could be made trafficking Texas cotton through Mexico for export through the Union Naval "anaconda" blockade. Not just to European mills and brokers, but to copper heads in New York, and thence to New England mills!
The Juáristas had a hodge-podge of arms, but the British Enfield was supposed to be the service rifle... So as Union forces seized such arms from CSA hands... South they went! As but one example, 30,000 stands of British arms in Baton Rouge, LA went to Juárez's forces. As for catle? the beeves supplied beef, hides/ leather, tallow and sinew to the taker: Mexicans, Imperialists, Indians, and Texans. Small wonder that the numbers increased. "Slow elk" to the Indians! ambulatory meat lockers to whoever drove them.
As for slavery, there was a tendency during the Civil War campaigns in the Mississippi Basin for slaveholders to "refugee" slaves in distant Texas... So the numbers increased in Texas during the war as well.
When Reconstruction ended early in Texas--and it did-- McNelly's Rangers was formed by Democrats in Austin. McNelly, dying of tuberculosis and having to chew rather than smoke his cigars, recruited many ex-Confederate cavalry raiders and even bushwackers into the Texas Rangers. Armed with .45-70 Sharps rifles and a passel of revolvers each, they moved south to the "Nueces Strip" to confront Cortinistas and lawless bandits and rustlers. (In?)Famously, they never made an arrest, but shot down and strung up anyone and everyone deemed outside the Austin-based law... In the case of Brownsville, bodies were stacked up in a pile, and anyone who came by to mourn was duly noted for a later nocturnal visit... Cortina was ultimately given the governorship of Tamaulipas but later moved to Mexico City under virtual house arrest. At least one of McNelly's Rangers--from Georgia--made the remark that Cortina considered many of the cattle north of the river those of his grandmother... And if the claims had been investigated, "he might have been right."
Such were the historical antecedents of the great cattle drives of the American West, and the "Golden Age of the Cowboy" after the Civil War.