Yes, Texas as a Republc, as a US State, and as a Confederate state was a slave state. Mexico had abolished slavery in 1826 and if a Texas slave could make it across the river they were free to become colonists in Mexico.
The Rio Grande.
The Rio Grande or Rio Bravo del Norte (as it's known in Mexico)
The Rio Grande is the river that divides the countries of Mexico and the United States of America. The river touches only one state in America - TEXAS. There are six states in Mexico that touch the river: Baja California, Sonora, Chihuahua, Coahuila, Nuevo Leon, and Tamaulipas.
The Rio Grande
The Rio Grande rises in the eastern part of the Rio Grande National Forest in the U.S. state of Colorado. The river is formed by the joining of several streams at the base of Canby Mountain, just east of the Continental Divide.
The explorer who first visited the U.S. river which is the largest within its state creating a natural boundary with Mexico is Juan de Oñate. He explored the Rio Grande, which is the largest river in New Mexico and forms a natural boundary with Mexico. Oñate's exploration of the Rio Grande occurred in the late 16th century as part of Spanish efforts to colonize and establish control over the region.
Texas, along the Rio Grande river.
The Rio Grande is the largest river of New Mexico, starting in the northern mountainous region of the state and winding southward through the middle until it becomes the border between Texas and Mexico. Other important rivers of New Mexico are the Canadian, Gila, Pecos and San Juan.
The Rocky Mountains dominate the central part of the state. The Rio Grande River flows through the state.
The boundary rivers of Texas are the Red River to the north, the Sabine River to the east, the Rio Grande to the south, and the Pease River to the west. These rivers help define the borders of the state with its neighboring states and Mexico.
New Mexico has two major bodies of water: the Rio Grande and the Pecos River. The Rio Grande forms part of the state's southern border and is one of the longest rivers in the U.S. The Pecos River flows through eastern New Mexico and eventually merges with the Rio Grande.