In the first chapter of my dystopian novel Sweet Grass, Rayner Dane drives south from Albuquerque, crossing into what locals call the Buffer, the short name for the Special Administrative Region of Arizona, New Mexico and Texas. As you can see in the map I've drawn, Mexico now owns the southern part of California, and smaller sections of three other states. I've included some city names so you can see roughly where the new border lies. The Buffer is jointly administered by Mexico and the United States. You can also see, up in Montana, I have also included a town called Sweet Grass, where most of the novel will be set. But my first chapters are set in Albuquerque and the Buffer. Here's a section from the third scene in Chapter One that provides a bit of backstory (from the first draft):
The official name for the Buffer was the Special Administrative Region of Arizona, New Mexico and Texas. A jurisdiction jointly administered by the governments of Mexico and the United States of America. Its northern border was a ragged arc descending from somewhere around Lake Havasu City to Galveston. The adjusted Mexican border was a parallel line anywhere between fifty and seventy miles south. What that meant in reality, Rayner was not exactly certain. What he did know is that while he was fighting with the International Brigades against beards in Sweden, and later in Somalia, Mexico annexed southern California and everything south of the Buffer. The resulting flood of internal migrants scrambling to take advantage of the good life quickly transformed what had once been one of the best places in the world into a toilet. If he thought the Buffer was decrepit, then American Mexico was its retarded inbred cousin. Whites entered at their peril. And those who had stayed on were a dying breed. Massacres of whites were such a frequent occurrence that the media had stopped reporting on them. Not that their demise upset him. Rayner’s sympathy for whites who thought they could coexist with low IQ foreigners expired with the fall of Sweden.