Much of the territory of the United States was, after all, settled by illegal squatters, hundreds of thousands of people who disregarded federal law in search of a better life for themselves and their families. Indeed, many of the current residents of Mississippi, Alabama, Indiana, Illinois and other states between the Appalachian and Rocky Mountains trace their roots directly to those one-time criminals we now laud as “pioneers.” Squatting, on both public and private lands, was also common in California and other Western states.

As I have written in the Washington Post (April 16, 2006), during the first half of the 19th century, the federal government hoped to use its vast Western territories to pay off the national debt by auctioning the lands to the highest bidders, typically Northeastern land speculators. Settlers making their way west to start a new life considered this policy to be a serious injustice.

Speculators often held land off the market for years, waiting for prices to increase. While federal law made it a crime to enter publicly owned land slated for auction, hundreds of thousands of squatters disregarded the law and trespassed on federal land (and also absentee-owned private land) to farm it illegally. Federal troops forcibly removed some squatters, but the illegal occupants usually reclaimed the land once the soldiers were gone.

Politicians, many of whom dabbled in land speculation, condemned the squatters’ lawless “usurpation” of public lands and “audacious defiance” in the face of Congress’s will. They accused squatters of being “greedy, lawless land grabbers who had no respect for law, order, absentee ownership of property and Indian rights.”

On Dec. 12, 1815, President James Madison issued a proclamation warning “uninformed or evil disposed persons... who have unlawfully taken possession of or made any settlement on the public lands... forthwith to remove therefrom” or face ejection by the army and criminal prosecution. But that didn’t stop the settlers. In 1838, Henry Clay, expressing a widely shared sentiment, dismissed the squatters as a “lawless rabble.” Once the squatters managed to sink down roots, though, the federal government found it difficult to remove them from the land. Accordingly, by 1837 Congress had, on 39 occasions, enacted retroactive amnesties for squatters occupying federal lands over the objection of people who argued that these amounted to a reward for lawlessness. These limited amnesties permitted squatters to purchase the land they occupied at a low price. Ultimately, the process of moving from occupation to landownership was fully legalized.

The 1862 Homestead Act granted free title to settlers who met the statute’s five-year-residency and improvement requirements. In one of the great ironies of American history, the lawless squatters underwent a dramatic image makeover to become, in the gauzy romanticism of our collective memory, heroic settlers.

The parallels between the controversy over illegal squatting by the ancestors of many white Americans and the current arguments over illegal immigration from Mexico and Latin America are significant. In both cases, poor people struck out for a new land to take for themselves the economic opportunity they believed they needed in order to provide a better life for their families.

And in both cases, they willfully disregarded laws that got in the way of their plans. Although willingness to flout the law is always cause for concern, the mere fact of lawbreaking should not keep legislators from making an independent assessment of the justice of the aspirations that push people to (nonviolently) engage in illegal immigration. Similar concerns did not stop 19th-century Congresses from assessing, and ultimately endorsing, the justice of the demands made by illegal squatters.

The legal doctrine of necessity, which traces its roots in the Western tradition at least as far back as the 13th century, makes it lawful for someone in extreme need to disregard the law in order to satisfy that need, as long as in doing so they do not inflict an even greater harm than the one they seek to avoid. Discussing the crime of theft, Thomas Aquinas said that “it is lawful for a man to succor his own need by means of another’s property, by taking it either openly or secretly.”

Although the doctrine has more recently been hemmed in by miserly judicial interpretation, its moral force remains compelling. After all, when the need motivating unlawful activity is sufficiently strong, it is unlikely that official repression will be able to stop it completely. And, as the Catholic moral tradition has long recognized, when the needs that push people to resort to illegal conduct are so great that they make lawbreaking justified or excusable, official repression itself becomes an act of lawless violence.

The squatters of the 19th century frequently ...