Question: When did American abolitionist, Kansas Territory Jayhawker, anti-slavery militant, and a friend of John Brown and Walt Whitman, member of The Immortal Ten, die?

Context paragraphs:
John Brown Museum: The John Brown Museum, also known as the John Brown State Historic Site and John Brown Cabin, is located in Osawatomie, Kansas.  The site is operated by the Kansas Historical Society, and includes the log cabin of Reverend Samuel Adair and his wife, Florella, who was the half-sister of the abolitionist John Brown.  Brown lived in the cabin during the twenty months he spent in Kansas and conducted many of his abolitionist activities from there.  The museum's displays tell the story of John Brown, the Adairs and local abolitionists, and include the original cabin, Adair family furnishings and belongings, and Civil War artifacts.

John Brown's raid on Harpers Ferry: John Brown's raid on Harper's Ferry (also known as John Brown's raid or The raid on Harper's Ferry) was an effort by armed abolitionist John Brown to initiate an armed slave revolt in 1859 by taking over a United States arsenal at Harpers Ferry, Virginia.  Brown's party of 22 was defeated by a company of U.S. Marines, led by First Lieutenant Israel Greene.  Colonel Robert E. Lee was in overall command of the operation to retake the arsenal.  John Brown had originally asked Harriet Tubman and Frederick Douglass, both of whom he had met in his transformative years as an abolitionist in Springfield, Massachusetts, to join him in his raid, but Tubman was prevented by illness, and Douglass declined, as he believed Brown's plan would fail.

John Brown's Body: "John Brown's Body" (originally known as "John Brown's Song") is a United States marching song about the abolitionist John Brown.  The song was popular in the Union during the American Civil War.  The tune arose out of the folk hymn tradition of the American camp meeting movement of the late 18th and early 19th century.  According to an 1890 account, the original John Brown lyrics were a collective effort by a group of Union soldiers who were referring both to the famous John Brown and also, humorously, to a Sergeant John Brown of their own battalion.  Various other authors have published additional verses and/or claimed credit for originating the John Brown lyrics and tune.

Walt Whitman Shops: Walt Whitman Shops (formerly known as Walt Whitman Mall) is a luxury shopping mall located in Huntington Station, New York on Walt Whitman Road (Route 110) and New York Avenue.  It has many stores including main anchors Bloomingdale's, Lord & Taylor, Macy's and Saks Fifth Avenue.  The mall is owned and managed by Melvin Simon and Associates, one of the largest developers of shopping malls in the United States and owner of Long Island's largest mall, Roosevelt Field in Garden City.  Suffolk County Transit, Nassau Inter-County Express and Huntington Area Rapid Transit all have bus routes that service the mall.

Walt Whitman High School (Bethesda, Maryland): Walt Whitman High School is a public secondary institution serving roughly the western part of Bethesda—an unincorporated suburban area of Washington, D.C., in Montgomery County, in Maryland.  The school is named in honor of the American poet, Walt Whitman.  Thomas W. Pyle Middle School feeds into Walt Whitman High School.

The Immortal Ten: The Immortal Ten were a group of militant Kansan abolitionists and Free-Staters who on July 23, 1859, freed John Doy from a Missouri jail, where he was being held for allegedly abducting slaves.  The group included George R. Hay, Silas Soule, Charles Doy, Capt. John E. Stuart [Stewart], S. J. Willis, Thomas Simmons, Joseph Gardner, Jacob Senix, Capt. Joshua A. Pike and Major James B. Abbott.

Thaddeus Hyatt: Thaddeus Hyatt (July 21, 1816 – July 25, 1901) was an American abolitionist and inventor.  In his opposition to slavery, Hyatt organized the efforts of abolitionists in Kansas to have the territory admitted to the Union as a free-state and campaigned for the federal government to aid Kansans afflicted by drought.  Hyatt befriended John Brown and provided Brown with financial support; following the raid on Harpers Ferry, Hyatt was investigated by a committee of the United States Senate.  When Hyatt refused to comply with a Congressional subpoena and cooperate with the Senate investigation, the Senate voted to jail the recalcitrant abolitionist.  As an inventor, Hyatt was a wealthy man, profiting from his invention of iron-and-glass vault covers for sidewalks and pavements.  Hyatt also innovated and patented several designs for reinforced concrete floors.

John Brown (abolitionist): John Brown (May 9, 1800 – December 2, 1859) was an American abolitionist who believed and advocated that armed insurrection was the only way to overthrow the institution of slavery in the United States.  Brown first gained attention when he led small groups of volunteers during the Bleeding Kansas crisis of 1856.  Dissatisfied with the pacifism of the organized abolitionist movement, he said, "These men are all talk.  What we need is action—action!"  During the Kansas campaign, Brown commanded forces at the Battle of Black Jack and the Battle of Osawatomie.  He and his supporters killed five supporters of slavery in the Pottawatomie massacre of May 1856 in response to the sacking of Lawrence by pro-slavery forces.

John Brown Farm State Historic Site: The John Brown Farm State Historic Site includes the home and final resting place of abolitionist John Brown.  It is located on John Brown Road in North Elba near Lake Placid, New York, where John Brown moved in 1849 to lead freed slaves in farming.  In 1855, he moved to Kansas to support his sons' efforts to keep Kansas as a free-state under the popular sovereignty laws, leaving his wife and several of his children behind.  Brown returned to visit his family at Lake Placid several times.  In 1859, Brown attempted to start a liberation movement among enslaved African Americans by seizing the arsenal at Harpers Ferry, Virginia (now West Virginia).  For this, he was tried for treason against the state of Virginia and was hanged.

Silas Soule: Silas Stillman Soule (July 26, 1838 – April 23, 1865) was an American abolitionist, Kansas Territory Jayhawker, anti-slavery militant, and a friend of John Brown and Walt Whitman.  Later, during the American Civil War, he joined the Colorado volunteers, rising to the rank of Captain in the Union Army.

Supporting paragraphs: The Immortal Ten Silas Soule
Answer: April 23, 1865