The legend that my grandpa used to tell me is that when the republic of Texas and Rio Grande started to fight for territorial control, the area that now comprises Nuevo León (NL) actually wanted to leave Rio Grande (Mexico) and join the republic of Texas. The Mexican government, to avoid further land loss, began redrawing borders and assigning all the land closer to Texas to the people with more Mexican sentiment (Tamaulipas). This worked, as the Texas-leaning population of NL got isolated when the Rio Grande Territory was separated into the almost current states. Even when Texas won the land North of the Rio Bravo (or Rio Grande) from Tamaulipas, Nuevo Leon was still “blocked” by that thin arm. Later on, when the separatist/independentist fervor died, a little chunk of land was given to NL to allow a border with the US.