Sen. Tom Cotton's New York Times op-ed article arguing for using the military to police violent protests and riots in American cities has elicited no end of outrage over its publication. This misses an important point: Modern law enforcement already deploys many tools and tactics borrowed from the military.

This "militarization" of policing has a long and troubled history. Anyone hoping to change how police do their work is going to have to reckon with it — and, in particular, how racial fears informed this transformation of policing in the first place.

The key shift came in earnest after World War II. Los Angeles's William Parker was the archetype of the new breed of police chiefs. He had served during the war and became a captain overseeing the military occupation of areas conquered by the Allies. When he returned, he transplanted many of the methods he had learned overseas to his hometown.

Parker despised the idea of "community policing," where officers lived among the people they policed. For Parker, policing was more akin to an occupation. The result of his reforms was a far less corrupt police force than the one he had inherited, but much more militarized department. Unfortunately, it was also overwhelmingly white, which led to an increasingly strained relationship with a city that had become far more diverse by the 1960s.

This set Los Angeles up for disaster. In the Watts riots in 1965, Parker reacted the only way he knew how. He described policing rioters as akin to "fighting the Viet Cong," as if city residents angry over racial injustices were a bunch of communist guerrillas. His deputy and soon-to-be successor, Darryl Gates, began taking officers to a nearby Marines training camp to bone up on adopting counterinsurgency tactics to the streets of Los Angeles.

This marked a sea change in policing. The historian Tracy Tullis has described how a growing number of city police forces came to view their restive populations as "a Vietnam at home," one the police could only tackle by embracing the tactics and increasingly the weapons of their military counterparts. As race riots became more commonplace over the course of the 1960s, counterinsurgency tactics became all the rage.

In Los Angeles, Gates created the first Special Weapons and Tactics team, which quickly became a model for other cities. The members of these SWAT units, most of whom had served in either the Korean or Vietnam wars, spent their days learning what Gates himself described as "the history of guerrilla warfare, scouting and patrolling, night operations, camouflage and concealment, combat in buildup areas [and] ambushes."

At the request of the Kerner Commission, which studied the causes of the 1967 riots in Detroit, Newark and beyond, Gates devised a "model civil disturbance plan" that could be distributed to police departments across the country. He proposed that departments be reorganized along military lines, and that officers start reading military manuals: "The Guerrilla and How to Fight Him" as well as "Combat in Fortified and Built-Up Areas." (Gates also recommended reading guerrilla warfare manuals by Che Guevara and Vo Nguyen Giap because cops needed to "know thy enemy.")

The embrace of military tactics went well beyond Gates. A growing number of think tanks, policymakers and defense analysts argued for training police officers in the latest, greatest tactics of counterinsurgency. Beginning in 1968, the Army began offering SEADOC: Senior Officers Civil Disturbance Orientation Course. This introduced high-ranking officers to a number of counterinsurgency tactics that could be used to contain restive civilian populations.

All of this has a distinct racial problem, as the communities on the receiving end of newly militarized police forces — to say nothing of the SWAT teams proliferating across the country — tended to be black or Hispanic. Proponents of militarized policing, though, insisted that it was the police who were the real victims. Parker himself declared at a civil-rights hearing that it was the police, not African-Americans, who "were the greatest dislocated minority in America today."

In 1968, that "minority" got a shot in the arm. Congress created a new entity known as the Law Enforcement Assistance Administration, which facilitated the transfer of military technologies for use by police forces. Until its demise in 1982, the LEAA gave police forces surplus military equipment, such as helicopters, body armor and armored vehicles, as well as sophisticated computer equipment and mapping tools.

The already blurry line between the police and the military became even more so in the 1970s, thanks to the so-called War on Drugs. Launched with great fanfare in 1971 by President Richard Nixon, this military-style assault on social problems spurred legislation that gave legal cover to "no-knock raids" and preventive detention. But it also paved the way for the use of military resources in domestic law enforcement, such as spy planes searching for drug fields. What the journalist Radley Balko has called the model of the "warrior cop" was now well established.

In 1981, Congress passed the Military Cooperation with Civilian Law Enforcement Act, which replaced the smaller LEAA. It enabled domestic law enforcement access to far more resources: more military equipment, supplies, bases and other assistance.

The trickle of military supplies then became a flood, thanks in part to the establishment of the "1033 program" in 1997. It formalized and expanded a set of existing programs designed to give police forces access to military supplies. It was specifically designed to help law enforcement agencies that made "counterdrug and counterterrorism requests." This became even easier to justify after the Sept. 11 attacks.

Since 2001, police departments have acquired everything from attack helicopters to grenade launchers, never mind more garden-variety weapons like M16 rifles. SWAT raids have also increased drastically. Little wonder that some commentators have in recent days blamed our current woes on the war on terrorism.

But that misses the deeper history of how cops came to act and look like their military counterparts — and how that process became entangled with race. Anyone hoping to fix this mess must reckon with the full sweep of that long, troubled history.

Stephen Mihm, an associate professor of history at the University of Georgia, is a contributor to Bloomberg Opinion. This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.