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Understanding the Constitution: How States May Respond to Illegal Immigration—Part I

Understanding the Constitution: How States May Respond to Illegal Immigration—Part I

To hear an audio version of this essay read by the author, please click here.

his essay was first published in the Jan. 8, 2024 Epoch Times.

As unauthorized foreigners continue to flood across the Southern border, state officials continue to cast about for solutions. In normal times, the federal government would remedy the problem. But these are not normal times: The administration of President Joe Biden actually seems to be aiding the influx.

State officials are hampered by a Supreme Court doctrine called “implied federal preemption.” The courts use this doctrine to void some state laws as contradicting federal statutes, even when the federal statutes do not explicitly override them.

For example, the Arizona legislature adopted four measures to address illegal immigration. They were consistent with the text of federal immigration statutes. In fact, they sought to further the purpose of those statutes. Yet the Supreme Court voided three of the four, even while admitting the damage illegal immigration was doing to Arizona (pdf). Similarly, the Montana Supreme Court struck down a voter initiative denying state services to illegal migrants. Montanans had approved the measure by a nearly 80 percent majority. But the court said it was “preempted” by federal immigration law (pdf).

The federal pre-emption doctrine has its place, but the courts have overextended it. One reason is the widespread belief in a constitutional myth. The myth is that the Constitution gives the federal government exclusive power over issues of foreign affairs, warfare, and immigration—and that the states have nothing to say on those subjects.

But anyone who reads the Constitution carefully can see that this is false. As this series will show, the document’s text explicitly recognizes some state military and immigration authority. The history surrounding the Constitution’s adoption tells us what that authority is.

It is true that in many cases, federal action may override state measures. But in other cases, the states may act irrespective of whether the feds approve.

This series summarizes state powers over immigration and military force—and particularly the power to respond to illegal border crossings. This series, and the research study on which it is based (pdf), may enable the judiciary to correct course.

“Invasion” in the Constitution

The noun “invasion” appears in the Constitution three times and the verb “invaded” once. Each time, the word triggers, or recognizes, a federal or state government obligation or power to respond. The appearances are as follows:

  • Each state has a militia. Congress may enlist state militias to “repel Invasions.” (Article I, Section 8, Clause 15).
  • An “Invasion” may give Congress authority to suspend the writ of habeas corpus (a traditional protection against imprisonment without trial). (Article I, Section 9, Clause 2).
  • The federal government is obligated to protect each state “against Invasion.” (Article IV, Section 4).
  • A state—independently of the federal government—may engage in war if “actually invaded, or in such imminent Danger as will not admit of delay.” (Article I, Section 10, Clause 3).

Obviously, a lot hinges on the meaning of “invasion” and “invade.”

What Does the Constitution Mean by “Invasion?”

Does the peaceful, but illegal, flood of immigrants across the border qualify as an “Invasion” as the Constitution uses the term? Put another way, are unauthorized migrants “invading” Texas, Arizona, and other states?

Today we use the words “invade” and “invasion” in several ways. Sometimes we mean a full-fledged military assault—as in the phrase, “the 1940 Nazi invasion of France.” But we use the word to cover non-violent actions: “He got so close, he was invading my space,” and “I think that law is an invasion of my rights.”

But—and this is critical—what is important for legal purposes is not how we use those words. What is important is how the Constitution uses them.

Three U.S. appeals courts have said that the Constitution’s meaning of “invasion” is limited to an attack by a foreign army. On the other hand, the Supreme Court once characterized a group of only eight spies as “invaders” (pdf).

But none of these tribunals actually investigated how the Constitution uses “invade” and “invasion.” Very few legal scholars—on whom judges often rely—have done so, either.

How to Find Out what “Invasion” Means

The first stop on the path to learning what the Constitution means by “invaded” and “invasion” is to look up those words in Founding-era (i.e., 18th century) dictionaries. I collected thirteen editions published between 1713 and 1789. Only one of the thirteen limited “invade” and “invasion” to formal military incursions. The other twelve included the military definitions, but also added definitions like “to intrude,” “to encroach,” and “to enter in a hostile manner.” I also checked the meanings of “intrude,” “encroach,” “hostile,” and other words used in describing “invade” and “invasion.” (For example, in this context “hostile” usually meant only “without permission”).

It was clear from the dictionaries that “invasion” covered much more than military assault.

The next stop on the journey consisted of the debates over the Constitution itself. They showed that the Constitution’s use of “invaded” and “invade” meant only physical intrusions, not intrusions on rights or personal space. Otherwise, though, the definitions were quite broad, as James Madison noted in Federalist No. 43. They certainly were not limited to attacks by foreign armies.

Madison himself, for example, wrote in Federalist No. 41 of attacks along the Atlantic coast by “licencious [sic] adventurers . . . daring and sudden invaders.” The phrase included not only formal military operations, but raids by pirates and other illegal opportunists.

The next step was to look more widely at 18th century discourse. It produced similar results. Moreover, the Founders’ books on international law all confirmed that people had no right to enter a sovereign’s territory without the permission of the sovereign. And no nation had the right to assist or allow its citizens to enter another sovereign’s territory without permission.

Some Founders Called Illegal Immigration “Invasion”

One of the most interesting pieces of evidence came from an actual 18th century case of illegal immigration.

Before the Constitution was adopted, the State of Connecticut had a claim to land in the Wyoming Valley. The Wyoming Valley is the part of modern-day Pennsylvania around Scranton and Wilkes-Barre.

Relying on their state’s claim, Connecticut citizens poured into the Wyoming Valley—to the great distress of Pennsylvania authorities. The newcomers settled on rich farm land that, according to Connecticut law, was theirs—but according to Pennsylvania law was not.

This immigration into the Wyoming Valley was not a military assault. Local Indians and Pennsylvania officials eventually attacked the settlers, and they resisted. But the immigration itself seems to have been almost entirely peaceful.

But to Pennsylvanians, the unauthorized immigration was an “invasion.” In 1754, Benjamin Franklin authored a plan “to divert the Connecticut Emigrants from their Design of Invading this Province.” And in 1783 the Pennsylvania legislature wrote to the Confederation Congress, labeling the Connecticut settlers “invaders of the State.”


The Constitution’s words “invaded” and “invasion” include unauthorized mass migration into the United States or into individual states. Unauthorized mass migration therefore triggers certain government powers and duties—state as well as federal. The following installments in this series will explain what those powers and duties are.


Rob Natelson