In 1864, the word was war.

On July 9, 1864, Maj. Gen. Lew Wallace’s Union troops confronted the Confederate forces of Lt. Gen. Jubal Early, en route to Washington via the Georgetown Turnpike, now Md. 355.

The Battle of Monocacy was a loss for the Union. Not only did the Confederates outnumber them 2 to 1, the Union faced some of the fiercest soldiers the South had to offer. The battle became the only Confederate victory on Northern soil. And once Wallace’s troops retreated, it seemed almost certain that Washington would fall, as Lt. Gen. Ulysses S. Grant had stripped the Union capital of its experienced troops in a risky campaign to take Richmond, Virginia.

But if 150 years of history and a nickname of “The Battle that Saved Washington” are any indication, Monocacy wasn’t the loss it appeared to be that July day.

Grant was in a bind in the spring of 1864. It was an election year, and President Abraham Lincoln was poised to lose, a figurative casualty of the Civil War. Grant’s forces had managed to contain Confederate Gen. Robert E. Lee in Richmond, but at the cost of 53,000 Union casualties. To make up for the loss, he took veterans forces from Washington, leaving only the disabled, the short-term fighters and militiamen.

Where Grant saw a problem, Lee and the Confederate leaders saw a way out of a siege.

“Lee has understood since the beginning of the war that the only way he’s going to defeat the North is by defeating the will of the Northern people,” said Gail Stephens, a historian and battlefield volunteer.

“It would be a huge deal for the Confederates to take the Union capital, even for a day.”

The Union troops didn’t stand a chance against Early’s army of about 15,000 veteran soldiers, sent out from Richmond at Lee’s request. From Lynchburg to Harpers Ferry, the Confederates drove off the opposition, taking ransoms and seeking to destroy Baltimore and Ohio Railroad lines and the Chesapeake and Ohio Canal along the way. The only major hiccup was access to their choice route to Washington, the Potomac River. The Union troops prevented passage by holding out at Maryland Heights.

Early then took the next best route to Washington — over South Mountain and down the Georgetown Turnpike.

At Monocacy, Wallace and his small group of soldiers waited nervously. He was there to protect the railroad bridge based on Grant-approved intelligence and the request of the B&O railroad president on July 4.

They had heard the rumors about Confederates on the horizon, but not much else. About 3,200 inexperienced troops was all they could gather, until Grant sent reinforcements from Petersburg, Virginia. Accounts vary, but Wallace’s total Union force was around 6,000 men.

Then, on July 7, Confederate and Union scouts clashed, and Wallace knew he needed to prepare for battle. In his journals, he wrote that visions of Washington in flames and an imperiled, fleeing Lincoln haunted his dreams.

On July 8, Union forces took their positions at the Monocacy Junction bridge and the Georgetown and Baltimore turnpikes. Two telegrams were sent that evening: First, Wallace pledged to fight as hard as he and his men could, warning of an attack on Washington to Maj. Gen. Henry Halleck, who then sent a telegram to Grant, seeking reinforcements.

Despite Wallace’s pledges, they were outnumbered when the Confederate forces attacked at 8:30 a.m. July 9. Their attempts weren’t enough to keep Early’s men from crossing the Monocacy, and that evening, they retreated toward Baltimore.

In the one day of battle, the Union troops had lost about 1,300 men, by Civil War Trust estimates. Though Early’s forces lost fewer men, the fighting took its toll on them, too. Hot, humid weather and days of marching weighed heavily as Early set off for Washington.

It’s easy to look at Monocacy’s numbers and dismiss the battle, Stephens said. At almost 2,200 casualties, it was no Gettysburg.

“A fair number of people really associate importance with size of battles and number of bodies, and that’s not necessarily true,” Stephens said. “Battles that are small can be as crucial as large battles, and this one was.”

It’s the battle that saved Washington. It’s the battle that wore down Confederate forces so that Grant and his men could regroup and send 10,000 reinforcements, salvaging Washington’s protections just as Early’s straggling army arrived at Fort Stevens on July 11. Shots were fired (one struck a man several feet away from Lincoln, who had come out as a spectator), skirmishes broke out, and blood was shed, but Washington remained under Union control as the Confederates turned back to Virginia on July 12.

“We didn’t have the disaster the capital might have received,” said Elizabeth Shatto, director of the Heart of the Civil War Heritage Area.

In the aftermath, Union supporters perplexed by the retreat feared it was the start of a much larger plan, though it proved to be the final Confederate invasion of the North.

“They seemed to accomplish all that they desired, and all that they were sent to accomplish, leaving the significance of the movement to be developed by the future,” according to Frederick’s Republican Citizen published July 15, 1864.

Still, Grant lauded Wallace for taking charge and recognized Monocacy’s significance for what it really was — a retroactive victory.

Grant wrote in his personal memoirs: “Whether the delay caused by the battle amounted to a day or not, General Wallace contributed on this occasion, by the defeat of the troops under him a greater benefit to the cause than often falls to the lot of a commander of an equal force to render by means of a victory.”

Follow Laura Blasey on Twitter: @lblasey.