Henry Warner Slocum was born on September 24, 1827, in Delphi Falls, New York, approximately twenty-five miles southeast of Syracuse. He was the sixth of eleven children born to Matthew Barnard Slocum and Mary Ostrander Slocum. Matthew Slocum, a native of Marietta, Ohio, operated a store in Delphi, which attached to the family home. When young Henry was not helping in the family store, he attended the public school in Delphi. Later, Slocum enrolled at Cazenovia Seminary in nearby Madison County, where he prepared for a career as a teacher.
In 1843, Slocum earned a certificate as a public school instructor and took a position as a teacher at a one-room school in nearby Woodstock. Using his wages, Slocum returned to Cazenovia, where he met and became engaged to Clara Rice. For the next four years, Slocum spent his time teaching, attending the Albany Normal School, and working at the family store.
U.S. Military Academy Cadet
In 1848, Congressman Daniel F. Gott secured an appointment for Slocum to the United States Military Academy. Slocum passed the entrance examination and entered the Academy on July 1, 1848. Among Slocum’s classmates were future Union generals, George Crook, Alexander McCook, and David S. Stanley. Slocum’s roommate during part of his stay at West Point was Philip H. Sheridan, who graduated one year after Slocum. During his four years at the Academy, Slocum proved to be an excellent student, graduating seventh in his class of forty-three cadets, on July 1, 1852.
U.S. Army Officer
Immediately following his graduation, the army brevetted Slocum to second lieutenant with the 1st U.S. Artillery and sent him to Florida to campaign against the Seminole Indians. Remaining in Florida only briefly, the army sent Slocum and his unit to Fort Moultrie at Charleston, South Carolina in 1853.
After arriving at Charleston, Slocum secured private quarters and then returned to New York, where he married Clara Rice on February 19, 1854. The couple remained married for forty years and produced four children, three of whom survived to adulthood.
Upon his return to Charleston for garrison duty, Slocum began studying law in his spare time. On March 3, 1855, the army promoted him to first lieutenant. A year later, hostilities with the Seminoles erupted again. When the army deployed Slocum’s unit to deploy Florida, Slocum resigned his commission on October 31, 1856.
Slocum returned to New York in 1856 and apprenticed with his brother-in-law in Syracuse, while he completed his law studies. He passed the bar examination in 1857. The next year, Slocum joined the New York State Bar, and he established a law firm with his nephew, Thomas L. R. Morgan, in Syracuse. While practicing law, Slocum also began speculating in real estate and other businesses.
Opposed to slavery, Slocum became active in politics as a member of the fledgling Republican Party while living in Syracuse. On November 2, 1858, voters from the Second District elected Slocum to a seat in the New York State Assembly.
As sectional tensions increased on the national stage, Slocum joined the New York State Militia in 1859. Commissioned as a colonel, he spent the next two years training the state’s soldiers in artillery tactics.
By the end of 1859, Slocum had his fill of Albany politics. He chose not to run for reelection to the state legislature. Instead, he returned to Syracuse, where voters elected him to the office of Onondaga County Treasurer.
Union Army Officer
Slocum served as Onondaga County Treasurer until the beginning of the Civil War, when the men of New York’s 27th Infantry Regiment elected him as their colonel. He received his commission on May 21, 1861.
Wounded at the First Battle of Bull Run
Mustered into service in the volunteer army on July 5, 1861, the War Department ordered it Washington, D.C., in time to take part in the First Battle of Bull Run (July 21, 1861). During the conflict, Slocum received a serious wound in his right thigh. After a brief hospitalization, Slocum returned home for six weeks of recuperation. While he was away from his regiment, officials promoted Slocum to brigadier general of volunteers on August 9, 1861.
Slocum rejoined his unit in Washington on September 10, 1861. During Major General George B. McClellan’s Peninsula Campaign (March 17–August 14, 1862), Slocum commanded the 2nd Brigade of the 1st Division of the 1st Corps of the Army of the Potomac from March until May. During the early part of the campaign, Slocum was engaged at the Siege of Yorktown (April 5-May 4, 1862). In May, McClellan chose Slocum to command the 1st Division of the 6th Corps. During the Seven Days Battles, Slocum’s men were engaged during the Battle of Gaines’ Mill (June 27, 1862), the Battle of Glendale (June 30, 1862), and the Battle of Malvern Hill (July 1, 1862).
On July 4, 1862, the War Department promoted Slocum to major general in the volunteer army. At thirty-four years of age, he was one of the youngest major generals in the Union army during the war.
Northern Virginia Campaign
At the conclusion of the Seven Days Battles, President Lincoln and General-in-Chief-of-Army Henry Halleck recalled the Army of the Potomac from the Virginia Peninsula on August 3, 1862. A few weeks later, Slocum’s division covered the retreat of Major General John Pope’s Army of Virginia, following the Confederate victory at the Second Battle of Bull Run (August 28 to 30, 1862).
Emboldened by the Rebel victory at the Second Battle of Bull Run (August 28 to 30, 1862), Confederate commander Robert E. Lee took the war to Northern soil in the late summer of 1862. On September 4, the Army of Northern Virginia began crossing the Potomac River, entering Maryland. On September 14, 1862, Slocum’s division attacked D. H. Hill’s division, guarding Crampton’s Gap through South Mountain. The Yankees quickly seized the gap and sent the Rebel defenders scurrying down the western side of the mountain. Despite Slocum’s success, his wing commander, Major General William B. Franklin, did not follow up on the Union victory in time to deter Lee’s advancement through Maryland.
12th Corps Commander
At the Battle of Antietam (September 17, 1862), Major General George McClellan, commander of the Army of the Potomac, held Slocum’s division in reserve. During the bloody engagement, Confederate forces mortally wounded the 12th Corps commander, Brigadier General Joseph K. Mansfield. One month later, on October 15, 1862, officials chose Slocum to replace Mansfield as the 12th Corps commander. At thirty-five years of age, Slocum became one of the youngest corps commanders in the volunteer army during the war.
In January 1863, Major General Joseph Hooker replaced Burnside as commander of the Army of the Potomac. In late April, Hooker divided his army into wings and started a plan to get to the rear of the Army of Northern Virginia. He placed Slocum in charge of the army’s right-wing, comprising the 5th, 11th, and 12th Corps.
Battle of Chancellorsville
On April 26, the right-wing crossed the Rappahannock and Rapidan Rivers. Slocum’s left-wing crossed the Rappahannock River downstream and entrenched when it encountered bad weather and nearly impenetrable thickets. Upon seeing the Union left wing stopped, Lee sent the bulk of his army against Slocum’s wing.
On May 2, Stonewall Jackson marched his corps of approximately 28,000 men around Hooker’s right flank. Late in the afternoon, Jackson’s troops slammed into the unsuspecting Union army, and the entire right flank collapsed within a quarter of an hour. Despite the huge numerical superiority of his army, Hooker lost his nerve and ordered his troops to fall back.
Slocum’s wing suffered a high number of casualties at the Battle of Chancellorsville, losing nearly thirty percent of its soldiers. Convinced that Hooker’s ineptitude was responsible for the severe losses, and for losing the battle, Slocum joined a group of Hooker’s subordinates who lobbied for Hooker’s dismissal.
Passed Over for Command of the Army of the Potomac
Hooker’s waning support and stubborn personality soon led to his demise. On June 28, 1863, Hooker attended a strategy meeting with President Lincoln and General-in-Chief Henry W. Halleck. When a dispute arose regarding the disposition of troops at Harpers Ferry, Hooker offered to resign his command. Lincoln quickly accepted Hooker’s resignation as commander of the Army of the Potomac and selected Major General George G. Meade to replace him. Although Slocum had more seniority than Meade (Slocum became a major general on July 4, 1862; Meade achieved the rank on November 29, 1862), Slocum’s relatively young age may have been a deciding factor in convincing the president to pass over him.
Battle of Gettysburg
Slocum’s first test under Meade’s command came at the Battle of Gettysburg (July 1-July 3, 1863). His actions on the first day of the engagement left him open to criticism from his peers and, later, from historians.
While marching his corps toward Gettysburg, Slocum stopped at a prearranged site roughly five miles southeast of town on the morning of July 1, despite claims from subordinate officers that there was clear evidence that a battle was being waged.
Starting at 1:00 p.m., Slocum received several requests from Major General Oliver O. Howard to advance to Gettysburg to support the 11th Corps, which was heavily engaged. Slocum vacillated and did not proceed toward Gettysburg until late in the afternoon, although he would have been the senior general on the battlefield. As a result, Slocum did not reach the town and take control of the forces there until nearly 6:00 p.m.—after the 11th Corps had suffered heavy losses. His dilatory behavior later earned Slocum the derogatory nickname, “Slow Come.”
Slocum commanded the troops at Gettysburg until approximately midnight, when Meade arrived on the scene. During the rest of the battle, Slocum and his men performed admirably. On the afternoon of July 2, when Meade ordered Slocum to deploy all the 12th Corps to the Union right, Slocum convinced Meade to allow him to keep one brigade on Culp’s Hill. The decision later proved to be beneficial, as Brigadier General George S. Greene’s brigade withstood several spirited Confederate assaults on the strategic elevation.
Following the Union victory at the Battle of Gettysburg, army officials detached the 11th and 12th Corps from the Army of the Potomac. The War Department sent them west under the command of Major General Joseph Hooker to support the Army of the Cumberland, which was under siege at Chattanooga, Tennessee.
Still sour from his experience at Chancellorsville, Slocum met with President Lincoln on September 28, 1863, and threatened to resign his commission if forced to serve again under Hooker. Sensitive to the possibility of losing a valued general, Lincoln promised Slocum a command independent of Hooker. Consequently, the War Department ordered Slocum to guard the Nashville & Chattanooga Railroad with one division of the 12th Corps. The rest of the 12th Corps fought with Hooker during the Chattanooga Campaign.
On April 27, 1864, with the endorsement of William T. Sherman and Ulysses S. Grant, the War Department assigned Slocum to command the Military District of Vicksburg. He held that position until August when he received command of the 20th Army Corps following the death of Major General James B. McPherson during the Battle of Atlanta. When the Georgia capital fell into Union hands on September 2, 1864, Slocum’s troops were the first to enter the city.
Savannah Campaign – Marching to the Sea
After occupying Atlanta, Sherman received approval from Grant to embark upon the “March to the Sea” that would make “Georgia howl.” On November 9, 1864, Sherman issued Special Field Orders No. 120, establishing the chain-of-command, objectives, and directives for the Savannah Campaign. Sherman divided his forces into two wings. Slocum commanded the left-wing, which comprised the 14th and 20th Corps, along with part of the Army of the Cumberland’s cavalry. These men met little resistance as they cut a swath of destruction from west to east across Georgia and captured the city of Savannah on December 21.
On February 1, 1865, Sherman embarked on a campaign through the Carolinas aiming to cut off supplies and reinforcements to Robert E. Lee’s Army of Northern Virginia facing Grant’s Army of the Potomac near Richmond, Virginia. Once again, Slocum’s forces served as the left-wing of Sherman’s army group.
Victory at Averasboro
On March 16, 1865, Slocum’s men attacked General Joseph Johnston’s entrenched Rebels north of Averasboro, North Carolina. Slocum’s soldiers flanked the Confederates, forcing them to withdraw to a second defensive line. The Grey Coats made a brief stand at the second line, before falling back to their third and final line of defense. Despite several Union assaults, the Confederates held their position until nightfall and withdrew to Bentonville under the cover of darkness.
Battle of Bentonville
By mid-March, Johnston had assembled an army of perhaps 21,000 soldiers at Bentonville. On March 19, 1865, Johnston made a stand, entrenching his army at Cole’s Plantation, blocking the road to Goldsboro. Once again, Slocum’s wing was the target. That afternoon, Johnston launched an assault on the Federals, forcing them to fall back temporarily. By nightfall, Slocum’s men checked the Rebel advance, and the first day of fighting at the Battle of Bentonville ended in a stalemate. On the next day, Federal reinforcements arrived, and Slocum gradually pushed Johnston’s men back. Johnston held on until March 21, when he withdrew during the night.
Army of Georgia Commander
A few days after the Battle of Bentonville, Sherman contacted General Grant requesting that the army separate Slocum’s wing (the 14th and 20th Army Corps) from the Army of the Cumberland and designate them as the newly created Army of Georgia. On March 28, 1865, the War Department issued General Orders No. 51 granting Sherman’s request. Under Slocum’s leadership, the Army of Georgia occupied Goldsborough and captured Raleigh in April. Slocum was also present on April 16, 1865, when Johnston surrendered the troops under his command to Sherman near Durham, North Carolina.
After Johnston’s surrender, Slocum led the Army of Georgia during the Grand Review of the Armies in the nation’s capital in May 1865. Afterward, he returned to New York on leave, before briefly commanding the Department of the Mississippi from June 29 to September 16, 1865.
On September 28, 1865, Slocum resigned from the army and returned to his home state and settled in Brooklyn, where he resumed his law career. In November 1868, voters of New York’s Third District elected Slocum to a seat in the U.S. House of Representatives as a member of the Democratic Party. Slocum served in the 41st and 42nd Congresses (March 4, 1869-March 3, 1873) but was not a candidate for reelection in 1872. Instead, Slocum returned to New York, where he founded the Brooklyn Crosstown Railroad, which later became the Brooklyn and Coney Island Railroad Company. In 1876, Slocum received an appointment as president of New York’s department of city works. He served in that office until 1883, when he returned to the House of Representatives for the 48th Congress (March 4, 1883 to March 4, 1885) as an at-large representative from New York. In 1893, Slocum retired as president of the Brooklyn and Coney Island Railroad Company.
In 1894, Slocum contracted a case of pneumonia in early April. Slocum died of heart failure caused by his illness on April 14, 1894, at his home in Brooklyn. His remains were interred at Greenwood Cemetery in the same city.