In early 1862, Union generals, soldiers and even the commander in chief of the Civil War were literally at a loss. Morale ran low.

Taking the oath of office in March 1861, President Abraham Lincoln of Illinois was a newcomer to the nation’s capital.

Compared to the flash-and-dash style of winning Confederate general Robert E. Lee, Lincoln was not a military man.

Lee, educated at West Point, was a career Union Army officer who chose to side with his state, Virginia, in battle rather than his riven country.

For that he’s a traitor, not a noble Southern gentleman, as he’s often portrayed by history’s lore.

But the contrast between Lincoln and Lee went much deeper than most know. Their conflict went beyond the political to the personal, to Lee’s homefront.

Lee owned and lived on one of the largest slave plantations in his state, right across the Potomac River. Arlington House and its thousand rolling acres, tilled by enslaved labor, was where he and his wife had their wedding in the parlor.

In a sweeping move in spring 1861, Lincoln had the strategy foresight to seize the entire Lee plantation, as well as the family mansion at the top of the hill overlooking Washington.

This foretold a time when the shrewd commander in chief of the Union Army would catch up and surpass Lee. The Confederacy won some of the first battles of the war and confidently predicted it would not last long.

Simply put, Lincoln’s mettle and character was widely underestimated at first, while Lee’s was overestimated — until the fateful Battle of Gettysburg.

Lee endured a three-day whipping after a rash decision to plunge north into Pennsylvania. That clash turned the tide on July 4, 1863. How apt.

Meanwhile, the scene at Arlington across the river changed dramatically. Lincoln and his top aides quickly turned it into a Union Army camp for training and drilling soldiers. William Tecumseh Sherman was given his general’s command in the former family parlor.

Arlington’s part in the Civil War also inspired its greatest marching melody. The Boston poet Julia Ward Howe rode over to the Union Army camp as an observer.

That night, she awoke in predawn darkness, inspired to pen the majestic lyrics to the “Battle Hymn of the Republic.”

(Howe chose the abolitionist tune of “John Brown’s Body” to go with her verses.)

“Mine eyes have seen the glory of the coming of the Lord / He is trampling on the vintage where the grapes of wrath are stored. …”

Howe gave Lincoln’s army a great galvanizing gift, a sense of righteousness that bordered on the biblical. The uplifting song ends with “Glory hallelujah / His truth is marching on.”

Boosting morale on her side of the Mason-Dixon line, Howe’s masterpiece was published in Harper’s New Monthly Magazine in February 1862.

Another arc connects the president and the poet: The Howes were guests at the Willard Hotel, where Lincoln had stayed before his inauguration.

Jamie Stiehm is a journalist and history buff. She can be reached at JamieStiehm.com.