Where is this?
It is the strip of S/W Texas from the Gulf of Mexico in the south to about Del Rio in the north, bounded by the Neueces River on the east and the Rio Grande on the west.
Why is this such a contested land?
This was the land where most, not all, but most of the large Spanish/Mexican/Creole land grants were located.
This land mass is about the only place, in Texas, that was purely Mexican/Spanish. It is fertile. It has water. It is a place that was/is productive.
Why contested?
In the treaty of 1836 with Mexico the boundry of Texas was set at the Rio Grande. This was conceded by Santa Ana in the treaty at San Jacinto when Texas won its indepence from Mexico.
What began this war?
First. Texas refused to recognize the land grants owned by the Spanish in Texas. The land was opened for settlment and the large land grants were broken up.
Mexico/some Mexicans refused this secession of this land. There was alarge amount of large cattle ranches in this area and some Mexicans had contracts with Cuba and others to supply beef to these folks.
These individuals would raid this area and take the beeves back to Mexico for shipment to Cuba.
Originally The Texas Rangers were organized as special Rangers to stop these raids and protect the border. R.I.P Ford was the commander of these Special Rangers until Texas became a state by treaty with the U.S..
After the Civil War, in about 1870, reconstruction had ceased and the carpet baging Republicans had been chased out of governement. The Rangers were again reorganized and a Company under Leander McNelly was assigned to protect the border and bring law to a land that was without law.
More detail later, this is an overview.
Blessings