On Monday, President Trump vowed, “We are ending the riots and lawlessness that has spread throughout our country,” threatening to send “thousands and thousands of heavily armed soldiers” to end the uprisings fueled by the police killing of George Floyd in Minneapolis on May 25. At roughly the same time, a mix of law enforcement agencies was using “smoke canisters, pepper balls, riot shields, batons and officers on horseback to shove and chase” peaceful protesters so Trump could walk to a nearby church for a photo op (though the administration denied this was the purpose).

Trump’s declaration jarred Americans and fostered widespread condemnation — and confusion. U.S. troops have been used sparingly on American soil in recent history — and not at all in the past 28 years — and some questioned whether Trump legally had the authority to approve such a deployment. Yet, despite the lack of recent precedents, the blurring of lines between civilian policing and military action dates back not to the civil rights era, nor even to Jim Crow, but to the very dawn of the American republic. The use of militaristic violence to contain civil disorder is a technique as old as the union itself.

America’s first police force was the militia. We now associate the word “militia” with groups of agitators protesting gun control in camouflage gear, but in the early years of the American republic, it had a different connotation. The militia was a volunteer civilian force made up of all able-bodied white male citizens between the ages of 18 and 45. They wore uniforms and met for training and inspections days, called “musters,” several times a year. According to a 1792 act of Congress, they also had to carry “a good musket or firelock,” “a bayonet” and “not less than twenty-four cartridges” suited to their chosen gun.

The militia’s official purpose was to maintain domestic law and order and, if necessary, to act as a first line of defense against foreign invasion. It was a hybrid between an emergency service, a modern police force and a volunteer army. Newspaper reports from the 1790s show the militia putting out carriage fires and intervening in disputes between customers and stall holders on market day.

But militiamen were also called upon to participate in military efforts and were often mixed in with U.S. Army troops during extended operations. Kentucky and Pennsylvania militiamen followed Gens. Josiah Harmar and Arthur St. Clair to the Ohio Valley in the early 1790s to wage war on Native American towns. In 1794, George Washington’s administration raised a force of more than 12,000 militiamen to suppress the Whiskey Rebellion, and in 1798, Secretary of War James McHenry used Army units alongside the militia to suppress another Pennsylvania tax revolt, known as Fries’s Rebellion.

In both cases, the violence had largely subsided by the time the troops arrived, and their presence caused as many problems as it solved. According to historian Paul Douglas Newman, both armies disrupted local surroundings by requisitioning vast quantities of food and firewood, threatening civilians, and even killing innocent bystanders.

As part of their job as defenders of “order,” militiamen were also essential to the regular policing of racial hierarchies in the early United States. In states with large enslaved populations, particularly in the South, the most important function of the local militia unit was to act as a slave patrol, shutting down gatherings of enslaved people and arresting those who were caught “strolling about from one plantation to another, without a pass from his or her master, mistress, or owner,” according to a 1792 Virginia law. The same law required militia units to report these “offenders” to a justice of the peace, who would sentence them to “any number of lashes, not exceeding twenty, on his or her bare back.”

Together with regular troops, militiamen also took part in brutally crushing slave rebellions like the 1811 German Coast Uprising in Louisiana.

Far from behaving as neutral enforcers of the law, militia units sometimes used moments of crisis to act out, violently, their own political desires. In 1798, a Federalist militia company in Lancaster County, Pa., used Fries’s Rebellion as an opportunity to beat up Jacob Schneider, a local Republican newspaper editor. The militiamen dragged Schneider from his home and whipped him in the market square of Reading, Pa., stopping only when forced by the arrival of a competing Republican militia company.

The political unreliability of local militia units troubled federal politicians in the 1790s and 1800s. The Haitian Revolution and the attempt by former vice president Aaron Burr to foment insurrection in the West heightened lawmakers’ fears of armed rebellion, be it by enslaved African Americans or by white dissidents. They worried that militiamen lacked the discipline and loyalty to enforce the law in periods of major crisis.

In 1807, therefore, Congress passed the Insurrection Act, which authorized “the employment of the land and naval forces of the United States, in cases of insurrection.” The law gave the president the power to use the Army and Navy to quash domestic unrest, legalizing the practice of mixing together militiamen and soldiers to put down revolts.

The first civilian police forces in the United States were established on a municipal level in the 1840s and 1850s, following the example of London’s Metropolitan Police (established 1829). These forces were designed to take over responsibility for preventing crime and disorder from the militia and the army. In theory, the demilitarization of American policing seemed to be complete with the Posse Comitatus Act, signed into law by President Rutherford B. Hayes on June 18, 1878. Under Section 15, Congress made it illegal “to employ any part of the Army of the United States … for the purpose of executing the laws” without the “authorization by the Constitution or by an act of Congress.”

This last clause constituted a very large loophole because Congress never repealed the Insurrection Act. As such, presidents have been able to use the U.S. military on dozens of occasions domestically, including by President Dwight D. Eisenhower to enforce a court order desegregating Little Rock High School in 1957 and by President Lyndon B. Johnson during the uprisings following Martin Luther King Jr.’s assassination in 1968. Most recently, President George H.W. Bush used it during the Los Angeles uprising in 1992.

While much has changed about the American military since the 18th and early 19th centuries — including its dramatic growth — in 2020 we still have a reserve militia and a separate professional military. Through a 1903 act of Congress, the militia of the United States was renamed the National Guard, which, over the course of the 20th century, has become far more efficiently militarized than the unreliable local companies of the 1790s. Many governors have called out the Guard in recent days in an attempt to restore order.

The Insurrection Act gives President Trump the power to deploy the U.S. military alongside the National Guard. But the question raised by history is not whether such a move would be legal — it’s whether deploying the Army against the protesters would do more harm than good. From the suppression of tax revolts in western Pennsylvania to the crushing of slave uprisings in the South, the use of military force for policing on American soil in the early United States came at a heavy cost, stoking fear and causing death and destruction. Leaders must ask themselves whether they are willing to risk causing more harm to American citizens already overburdened with economic instability, the coronavirus pandemic and ongoing racist violence.