What does Article IV, section 4 of U.S. Constitution mean & how's it relate to our southern border.?

Quoting: "The United States shall guarantee to every state in this union a republican form of government, and shall protect each of them against invasion; and on application of the legislature, or of the executive (when the legislature cannot be convened) against domestic violence."

What it means is that states must have electoral processes to pick an executive and a legislature -- these cannot be hereditary, or the result of winning a lotter (though elections often seem like it).

The domestic violence clause allows the states to call for federal assistance if there is armed revolt against the state govt.

The invasion clause makes the federal govt responsible for ensuring that hostile forces do not invade (attack), and at an invasion of any state is an invasion of the country.

While I see your point, neither of these has any bearing on the immigration issue. We're not seeing immigrants rolling in with tanks and assault rifles. So, it's not a military invasion.

What you're really talking about is the Article I power to regulate when and how private individuals can come into the country. And the federal government has exclusive authority to do that.

So let me get this strait coragryph... because the invaiders are poorly armed or fitght in an unconventional mannor, they dont count? To point out the obvious, the 9-11 hijackers didnt have tanks either you twit.