On Dec. 11, the Department of Defense announced that it would again allow transgender citizens to enlist in the military starting on Jan. 1, 2018, ending months of uncertainty after President Donald Trump announced a ban on transgender troops in a July tweetstorm. The rebuke of Trump’s ban came after a federal judge againdenied a White House request to delay the enlistment of transgender recruits, due to the administration’s claims about its potential impact on the U.S. armed forces. After months of litigation, it’s possible the Supreme Court will end up finally deciding the future of transgender recruits.

In the decades since Bill Clinton’s 1992 election-day pledge to end the Pentagon’s ban on gay service members, one refrain in conservative circles has remained constant since then-Nebraska Republican senator and future defense secretary Chuck Hagel helped coin during the “Don’t ask, don’t tell” debate of 1999: “The U.S. armed forces aren't some social experiment.”

Hagel ended up eating his words when he came out in support of women in combat roles as a “civil rights issue” 15 years later, but the maxim has persisted. After Donald Trump’s surprise 2016 victory, some military experts said they believed the Pentagon would finally abandon the “social experimentation” of the Obama administration on the watch of retired Marine Gen. James Mattis.

But despite conservatives’ ostensible emphasis on history and tradition, their refrain is deeply inaccurate: The armed forces have, by necessity, always served as a petri dish for broader cultural change in America — even before the country’s inception.

The US Military Has Always Been A Social Experiment

At dawn on June 17, 1775, British Gen. William Howe ordered fire on American forces three times and drove them northward across Bunker Hill. In this battle, the Americans had 400 dead and wounded men; the British lost more than 1,000. Freed slave Peter Salem was credited with the shot that killed British Maj. John Pitcairn.Photo via U.S. Army

A revolution in war

In its earliest moments of life, the American state was fiddling with the demographics of its armed forces. In 1776, newly minted Continental Army commander George Washington removed the elected officers who had traditionally represented the colonial militias, replacing them with hand-picked officers who would conform to the rigor and discipline he adopted during his stint as a regular British Army officer. Washington knew that only through the now-familiar standards of good order and discipline could an American military force actually flourish. “I am … disturbed at the conduct of the militia,” Washington wrote in a letter dated Sept. 30, 1776, “whose behavior and want of discipline has done great injury to the other troops, who never had officers, except in a few instances, worth the bread they eat.”

Related: A Brief History Of The US Military As An American Social Experiment »

Order and discipline were only part of his agenda, though. After initially prohibiting the recruitment of African-Americans, Washington reversed course when his army fell apart during the brutal winter of 1777–1778 in Valley Forge. Some units — like the 1st Rhode Island “Black Regiment,” staffed by 140 slaves who enlisted in exchange for their freedom — were segregated. But enlisted African-American freeman also served in integrated units; at least 5,000 are confirmed to have served, with estimates suggesting African-Americans at times comprised 12% of the Continental Army — “the most integrated that the Army would be until the Korean War,” according to Army historian Maj. Glenn Williams.

This “social experiment” was, of course, driven largely by necessity; African-Americans were again prohibited from joining the Army or Marine Corps after 1790 — not the Navy, where many served as sailors during the disastrous War of 1812. Even Andrew Jackson raised two battalions of African-American soldiers for the Battle of New Orleans in 1815, the last major confrontation in the conflict with Britain. The openness to build an integrated force in times of need reflected American commanders’ desire to advance a strong nation united in common defense of its Constitution.

The US Military Has Always Been A Social Experiment

Soldiers with Company E, 4th United States Colored Infantry. Theirs was one of the detachments assigned to guard the nation's capital during the American Civil WarPhoto via Library of Congress/Wikimedia Commons

Equality in combat

By the outbreak of the Civil War, staffing needs and pressure from abolitionists drove the Union to once again authorize the enlistment of black soldiers. After Congress passed the Second Confiscation and Militia Act on July 17, 1862, African-American volunteers quickly filled the ranks of segregated regiments, lured by the promise of full citizenship. According to the National Archives, some 179,000 African-American men served in the 175 United States Colored Troops (USCT) regiments — a full 10% of the Union fighting force. Another 19,000 served in the Navy. Eighty of those African-American service members were NCOs.

Despite their commanders’ preference for segregated regiments and an aversion to deploying African-American personnel downrange, black infantrymen proved their worth on the battlefield in crucial engagements from Louisiana to South Carolina. By the conclusion of the conflict, some 16 African-American soldiers (and 8 sailors) had earned the Medal of Honor — including freed slave William Harvey Carney from the 54th Regiment of Massachusetts Volunteers, who carried the colors during the infamous July 1863 assault on Fort Wagner, South Carolina, immortalized in the movie Glory. Women, too, contributed informally to the war effort in reconnaissance and intelligence roles; most famous among them was Harriet Tubman, who served as a scout for the 2nd South Carolina Volunteers.

The US Military Has Always Been A Social Experiment

A Union recruitment broadsidePhoto via Library of Congress/DoD

Even before the end of the Civil War, the Union Army quickly embraced the fruits of its social experimentation. One year after standing up black regiments, the Union had established the Bureau of Colored Troops to oversee the fast-growing ranks of African-American infantrymen; by 1864, Congress established equal pay for African-American troops, including those who had fought for the Union since 1862. The pay decision wasn’t born out of some thought experiment about equality and liberty, but concerns over troop morale and readiness: African-American soldiers of the 55th Massachusetts had waged war with Congress overcompensation, a sign to lawmakers of possible instability in the ranks. (Those soldiers earned their keep: Just weeks later, members of the 55th valiantly laid down their lives during a disastrous Union rout at Honey Hill, South Carolina.)

Southern states, of course, spent the post-war years building a new regime of oppressive Jim Crow laws, but the Department of War didn’t abandon its social experiment once hostilities ceased. African-American troops comprised a significant portion of the Union’s southern occupying force during Reconstruction, and Congress stood up six regiments of so-called “Buffalo Soldiers” in 1866 to maintain order in the American West and maintain order during the Spanish-American and Philippine wars.

Though they were frequently kept from combat and overseen by white officers, their service paved the way for future civil rights victories for African-Americans. Former slave and abolitionist Frederick Douglass put it best: “Once let the black man get upon his person the brass letter, U.S., let him get an eagle on his button, and a musket on his shoulder and bullets in his pocket, there is no power on earth that can deny that he has earned the right to citizenship.”

The US Military Has Always Been A Social Experiment

Soldiers with the 369th Infantry Regiment, formerly known as the 15th New York National Guard Regiment, who won the Croix de Guerre for gallantry in action.Photo via National Archives/Wikimedia Commons

The “new social bargain”

The Union Army’s social experiment with African-American regiments laid the groundwork for what historian Richard Slotkin called “a new social bargain” to the huddled masses of European immigrants streaming into the country ahead of World War I: Serve your country, and your country will serve you — with full citizenship. The result was the Foreign Soldier Service, a military organization designed as a training pipeline for foreign-born soldiers centered on American civics, culture, and language. It was a crucible for American assimilation at a time when xenophobia and anxiety ran high.

As in the Revolutionary and Civil wars, the expanded recruitment was once again driven by manpower deficits; with conflict in Europe on the horizon, the U.S. government had to quickly raise a standing Army of millions. But the social experiment, according to Slotkin, also reflected the changing composition of the American body politic:There was no way to build that force “without enlisting large numbers of African-Americans and immigrants or ‘hyphenated Americans,’ a derogatory term for immigrants first used at the turn of the century,” he explains. “It was in this crisis that American leaders rediscovered the ideals of civil equality that late 19th-century ethnonationalism had called into question.”

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By the time the Treaty of Versailles brought the Great War to a close, half a million immigrants from 46 nations had fought in the U.S. armed forces — a whopping 18% of the country’s fighting force — in pursuit of expedited citizenship, according to the National Park Service. They fought alongside 350,000 African-Americans who served with the American Expeditionary Forces, including the 42,000 assigned to the 92nd and 93rd Divisions infantry units that fought during World War I alongside French troops.

Just as African-American soldiers introduced broad swaths of the country to African-American citizens, immigrant soldiers gradually earned understanding and empathy from the American service members in their units.“The Greeks, Irish, Poles, Jews, and Italians who were in my platoon… They were my buddies,” legendary World War I Army legend Alvin “Sergeant” York said. “I jes’ learned to love them.”

The US Military Has Always Been A Social Experiment

Tuskegee airmen in North Africa circa May 1942Photo via National Archives/DoD/Wikimedia Commons

A world at war

Between World War I and II, African-Americans were initially “denied military leadership roles and skilled training because many thought they lacked qualifications for combat duty,” according to the Air Force Historical Studies Office. Part of the African-Americans’ plight stemmed from a 1925 Army report that deliberately misrepresented the performance of African-American soldiers during World War I, in an eerie predecessor to our modern “social experiment” rhetoric: “The War Department,” the report stated, “has no adequate defense against political and racial pressure and was forced to organize negro combat divisions and commission unqualified negro officers.” Many of the fears were purely cultural: Gen. Henry H. Arnold, commander of the Army Air Forces, feared an “impossible social problem” should African-Americans end up in command of white troops.

But that changed in 1940 after President Franklin Delano Roosevelt announced the creation of an African-American aviation squadron known as the Tuskegee Airmen, which never lost an Allied bomber amid frequent sorties across North Africa and the Mediterranean. Despite Arnold’s previous fears, the Army Air Corps went from all-white to hosting tens of thousands of African-Americans personnel across every specialty in a publicity victory that, as one historian put it, “prove that blacks could master the most complex and dangerous machinery.” It’s partially thanks to their valor that the circumstances allowed President Harry Truman to issue Executive Order 9981 in 1948, mandating the full racial integration of the U.S. military.

Related: The Tragic And Ignored History Of Black Veterans »

Once again, the military embraced social experimentation out of necessity, precipitating social change in the civilian world home. “The crisis of mobilization for World War II created the opportunity for social change that had been squandered after World War I,” Slotkin observed. “Once again the large-scale enlistment of black and ethnic minority soldiers was a necessity… The resemblance of Nazi race laws to the segregation and exclusion enforced by Jim Crow helped discredit the South’s racial regime with a broad public.”

The US Military Has Always Been A Social Experiment

In this March 15, 2015 file photo, U.S. Rep. Seth Moulton, D-Mass., center without hat, marches with members of OutVets, a group of gay military veterans, during the St. Patrick's Day parade in Boston's South Boston neighborhood.Photo via Associated Press

The (next) greatest generation

In the years since Executive Order 9981, the culture of the U.S. military has lagged behind the newly-constituted Department of Defense’s vision of equal opportunity. Three months before Truman officially signed the order, Army Secretary Kenneth Royall deemed Truman’s order “an instrument for social evolution” that would ruin the morale of white soldiers.

But those conservative worries are more symptoms of xenophobic panic rather than empirically sound evaluations of performance. A 2003 examination found that the U.S. armed forces experienced no negative effects on readiness or effectiveness when lawmakers and presidents embraced inclusion, from the Civil War to Vietnam. Research published in 2012 found that one year after the repeal of ‘Don’t Ask, Don’t Tell’ in 2011, the integration of openly gay service members had yielded virtually no impact on unit cohesion and troop readiness. A DoD study on gender integration recommended that the Army not only continue incorporating female service members into all MOSs, but identified sexual assault and sexual harassment by their male colleagues as a more important risk factor regarding unit morale, cohesion, and readiness. Recent studies addressing the transgender recruit controversy have yielded similar results: According to a 2016 RAND report, the several thousand transgender service members estimated as currently serving in the armed forces have had a “minimal impact on unit cohesion.”

Related: Here Are All The Nations In The World That Let Transgender Troops Serve »

Worries about manpower and readiness are even more important now, as the Global War on Terror continues to stretch the U.S. armed forces. And these pressures come as the armed forces face unprecedented obstacles in recruiting in a country defined by a hellish political landscape and aggressively flabby recruiting pool.

For the military to take on all enemies, it must enlist “any American who wants to serve our country and is able to meet the standards should have the opportunity to do so,” as Sen. John McCain recently put it. To exclude would-be troops, in spite of their capacity to kill and break things, isn’t just empirically wrongheaded on the part of those conservatives — it’s a more dangerous social experiment than any inclusive policy they’ve ever fought.