Explained | What is the US National Guard?

Several hundred soldiers were deployed to the streets of Los Angeles on Sunday, as demonstrations against President Donald Trump's immigration crackdown raged for a third day. The troops were members of the California National Guard, called in by the president against the wishes of Gov. Gavin Newsom.

Not since 1965 has a president summoned a state's National Guard against the will of a governor. Trump cited a rarely used law enabling him to bypass the governor in the event of "a rebellion or danger of a rebellion against the authority of the Government of the United States." Newsom called the move a "serious breach of state sovereignty" and asked Trump to reverse his order.

The National Guard is a state-based military force made up of hundreds of thousands of trained soldiers who live in communities across the country and typically serve only part time. Most hold civilian jobs or attend college.

All new recruits must pass basic training. Once they're in, they participate in regular drills, usually one weekend each month, and a two-week-long training each year. The tradition of state-based militias is older than the nation itself. The National Guard traces its history to 1636, when the legislature of the Massachusetts Bay Colony formally organized its militia into regiments. Militias composed of nonprofessional civilian soldiers played a critical role in the Revolutionary War and, when the first standing American army was established in 1775, state militias continued to exist alongside it.

Guard troops are activated only when they need to be -- most often during natural disasters, wars or civil unrest. Both governors and the president have the power to activate the National Guard. A president's decision to activate the Guard often comes at the request of state or local officials. In 1992, President George H.W. Bush did so in response to the Rodney King riots after California's governor asked him to.

At Sunday's protests in Los Angeles, National Guard troops appeared to largely refrain from engaging with demonstrators, even as federal immigration and homeland security officers and the city police fired crowd-control munitions at the protesters.

Before this weekend, a president had not overridden the state's governor to send the National Guard in to quell civil unrest since 1965, when President Lyndon B. Johnson deployed the Alabama National Guard to protect civil rights marchers in Selma, Alabama.

More often, governors activate the Guard to help respond to urgent circumstances at the state level, like severe weather. In January, Newsom activated at least 1,680 members of the California National Guard to help secure evacuation zones after fires ripped through Los Angeles. Thousands of Guard members responded to Hurricane Katrina in 2005. And hundreds helped direct traffic, search for survivors and battle the flames during a devastating fire in Lahaina, Hawaii, in 2023.

The National Guard has two parts: the Army Guard and the Air Guard. Each functions as the main reserve force for the associated branch of the military, and troops can be deployed overseas to support military operations abroad. Guard members played a major role in the Iraq and Afghanistan wars: At one point in 2005, the National Guard made up more than half of all American combat brigades in Iraq, according to a fact sheet published by the Guard. More recently, the Guard has also helped train and support the Ukrainian military.