Imagine it. It's the worst-case scenario for some people—immigrants of different skin color stream across an unprotected border, searching for a better life. With them, they bring the lifestyles of their home country. Unfortunately, their host country had laws banning the practices. After some time, the host country moves to enforce the federal laws of the land. The newcomers successfully resist the authorities with violence. After successfully defying federal law enforcement, the immigrants become separatists and declare an independent state. The situation worsens when the immigrants' home country decides to annex the newly independent state. A war between the countries ultimately ensues.
Is this a white supremacist's worst nightmare? Hardly. Check your history books, albeit not ones approved in Texas public schools. It is the birth story of the state of Texas. The federally illegal practice that the immigrants bring with them? It's slavery, introduced by Americans moving into what was northeast Mexico.