When early empires fell, I doubt that everyday citizens knew or cared until the death, disease, chaos and lack of means to survive were at their doorsteps.
When (not if) the global and national structures collapse, there will be regions, cities and towns that will persevere because they're self-sufficient.
They're not immigrants, they have no desire to become Americans. Big Democrat Party wants them citizens so they can eternally elect Democrats. Big Business wants cheaper high tech labor and I have no clue what they want with 10's of millions of non-English speaking, illiterate, uneducable, underclass infiltrators. They never say why they want these people other than "immigration" helps the economy. These 10's of millions of people cost our economy. What's up with the US Chamber of Crony Capitalists?