There is an extremely dangerous “invasion” happening now at the U.S. southern border.

Even this is a controversial statement. On Monday, Democratic New York Rep. Jerry Nadler described the idea that mass border crossings constitute an “invasion” to which Texas is legally entitled to respond as a “crackpot legal theory.”

Setting aside questions of scale, I want to demonstrate here that even a little bit of illegal immigration by people who are merely seeking a better life qualifies as an “invasion” as that word is used in the U.S. Constitution, so long as we avoid putting a modern spin on the original meaning that was intended by the Framers.

Let’s start with Benjamin Franklin, who was the senior figure during that hot Philadelphian summer of 1787. In 1754, Franklin had authored a plan which he said would “divert the Connecticut Emigrants from their Design of Invading this Province.” For Franklin, unwelcome immigrants equaled invaders. Likewise, in 1783, the Pennsylvania legislature labeled the illegal Connecticut settlers as “invaders of the State.”

Thus, mere immigrants and settlers could qualify as “invaders” if they had no permission to barge into a colony (or pre-constitutional state) without permission. And the invaded state could use force against the peaceful invaders, as Pennsylvania did in the so-called Pennamite War against the unauthorized immigrants from Connecticut.

Franklin’s colleague James Madison of Virginia had a similar understanding. Madison did as much as anyone to shape the federal Constitution, and he wrote in 1788 about the clause promising federal protection against invasion (see Article IV, Section 4). According to Madison, “The latitude of the expression here used, seems to secure each state not only against foreign hostility, but against ambitious or vindictive enterprises of its more powerful neighbors.” 

The historical evidence is almost endless that the word “invasion” did not require any armed invasion by a government. For example, a 1758 essay explicitly discussed an “invasion by a fleet of unarmed flat-bottomed boats” in the context of denying that such a threat was serious enough to justify a large navy. Notice that word: “unarmed.”

The Constitution (in Article I, Section 10) authorizes a state to wage war against any such invasion. Of course, that is not a license to slaughter unarmed civilians; it was well understood as a matter of international law in the 1780s that lethal force could not be used against unarmed people. But nonlethal force could.

Up until the Revolution of 1776, our states were part of the British Empire. People who immigrated illegally into the British Empire in the eighteenth century were technically considered “alien enemies” who were not entitled to any protection, nor entitled to pay allegiance to the crown, unless the government decided to receive them into the society that they had invaded. These historical understandings were baked into our Constitution, and remain applicable today (though we are always free to change the Constitution to get rid of borders; Article V lets us change whatever we would like). 

Another significant point is that the size of an invasion was pretty much irrelevant to whether it qualified as an invasion, within the original meaning of the Constitution. A member of parliament said in 1742 that, “a small Invasion may be as fatal in its Consequences as the most formidable and most successful Invasion at another Time.” There was an effort during the ratification of the Constitution to put aside small invasions, because an “invasion, however small, tak[ing] place, in Georgia” should arguably not trigger war measures as far away as Massachusetts. But that effort to distinguish between large and small invasions was rejected, probably because everyone agreed on the importance of nipping any invasion in the bud.

As a lawyer and history buff, I enjoyed looking into the original historical meaning of these parts of the Constitution, along with my colleague, Professor Rob Natelson. We invite you to take a look at our further evidence and conclusions in a forthcoming law review article that is already available for free on the internet.