Once the rebels succeeded in breaking Texas away from Mexico and establishing an independent republic, slavery took off as an institution. . . .

As more [enslaved people] came into the Republic of Texas, more escaped to Mexico. Matamoros in the 1840s had a large and flourishing colony of [formerly enslaved people] from Texas and the United States. Though exact numbers do not exist, as many [enslaved people] may have escaped to Mexico as escaped through the more famous underground railway to Canada. The Mexican government, for its part, encouraged the [formerly enslaved] runaways, often with offers of land as well as freedom.

– James W. Russell, Slavery and the Myth of the Alamo