President Donald Trump is considering the mobilization of up to 100,000 National Guard troops to round up unauthorized immigrants, the Associated Press reported Friday. (The White House has denied the report). The news service acquired a draft memo written by Homeland Security Secretary John Kelly that proposed using Guard troops to enforce immigration laws across 11 states, including Oregon, Nevada, Utah, Colorado, Arkansas and Louisiana, states far from the Mexican border. 

The National Guard, which traces its origins to 17th century Salem, Massachusetts, is one of five branches of the military, along with the Army, Navy, Marine Corps, Air Force and Coast Guard. The Guard is a reserve military force, tasked with protecting the U.S. citizenry, and is broken into state organizations that include the District of Columbia, Puerto Rico and Guam. Individual state National Guard units are controlled by governors of those states, but they can be activated by the president, as well. 

While National Guard units can be deployed throughout the world to engage in military operations, the Guard is usually deployed domestically to respond to natural disasters. In October, for example, thousands of guardsmen were deployed throughout the Southeast to help with evacuations when Hurricane Matthew hit the coast. Last year, the National Guard helped respond to a water crisis in Flint, Michigan. After Hurricane Katrina, 35,000 guardsmen and active-duty troops were deployed to the Gulf Coast. 

It's much more unusual for the National Guard to be used in law enforcement activities, although the Guard has been used in border enforcement activities in the past. Below is a brief history of six times the National Guard has been deployed domestically to law and order.

Standing Rock, North Dakota

North Dakota Gov. Jack Dalrymple activated 100 National Guard troops in September in advance of a judge's ruling on the North Dakota Access pipeline, which became a flash point for Native American rights and drew thousands of protesters to a campsite on the pipeline route.  The judge subsequently ruled against a request from the Standing Rock Sioux Tribe to issue an injunction against the construction of the pipeline. After more than a month of legal wrangling, the National Guard teamed with local police and conducted a raid of the protesters' encampment, arresting 140 people. In January, the North Dakota Guard deployed two surface-to-air missile-launchers near a pipeline work site, but a spokesman said the systems were unarmed and used for only for their observation capabilities. 

Ferguson, Missouri

In the fall of 2014, Gov. Jay Nixon sent the Missouri National Guard to Ferguson, Missouri after riots and protests erupted in the St. Louis suburb  over the shooting death of unarmed black man Michael Brown at the hands of white police officer Darren Wilson. After initially deploying 700 troops, Nixon upped the total to 2,200 after rioters looted and burned local businesses despite the Guard's presence in the city. Nearly a year later, documents revealed that the guard referred to protesters as "enemy forces" and "adversaries," angering some residents and local politicians

Los Angeles

After four white LAPD officers were acquitted in the beating of Rodney King in 1992, nearly 10,000 California National Guard troops were dispatched to Los Angeles to stop riots and looting that eventually killed 50 people and injured 2,000. Gov. Pete Wilson initially declared a state of emergency and deployed 2,000 guard troops before increasing the deployment as the riots raged for several days. During the riots, some residents reported the National Guard was harassing black residents

Miami

The Florida National Guard responded to riots in Miami in 1980, after insurance agent Arthur McDuffie died following a beating from white Dade County police officers. McDuffie, a black man, led police on a motorcycle chase before surrendering, raising his hands and telling police "I give up," according to the Sun-Sentinel. The riots eventually left 18 people dead. 

Kent State University

In perhaps the most infamous case of the National Guard deploying against U.S. citizens, the Ohio National Guard was deployed to Kent State University in 1970 to quell student protests against America's invasion of Cambodia during the Vietnam War. The guard ordered the crowd of student protesters to disperse, and eventually fired tear gas canisters at the students, CBS News reported. Students responded by throwing rocks and tear gas canisters back at the guardsmen, and in the chaos, the Guard opened fire, killing four students and wounding nine more. 

Little Rock, Arkansas

In 1957, Gov. Orval Faubus used the Arkansas National Guard to prevent black children from entering Little Rock Central High School, in defiance of the Supreme Court's Brown v. Board decision that ruled segregated schools illegal. President Dwight Eisenhower responded by taking control of the Guard from Faubus, and deploying it to protect the black children integrating the school.