[4] Abbott was engaged at the center of several key Civil War battles and was widely known and admired for his leadership, courage and composure under fire.

[9] The young Henry found the rigid atmosphere at Harvard "irksome" and was frequently admonished for "indecorum at prayers," "neglect of mathematics," and "tardiness at recitation.

[13] The first commander of the 20th Massachusetts Infantry Regiment was Colonel William Raymond Lee, a United States Military Academy graduate and professional soldier.

[13] On October 21, 1861, Abbott's 20th Massachusetts Volunteer Infantry Regiment was ordered to cross the Potomac River from their camp at Poolesville, Maryland and with other Union Army units to make a demonstration towards Leesburg, Virginia.

[16] Despite Abbott's brave attempt to hold the line, the 20th Massachusetts Infantry and other Union troops were steadily forced back.

[20] After rebuilding its strength for four and one-half months at Poolesville, Maryland, the 20th Massachusetts Volunteer Infantry Regiment took part in the Peninsula Campaign.

[22] On June 30, 1862, Abbott was wounded in the right arm at the Battle of Glendale, Virginia,[3] which compelled him to leave the regiment temporarily in order to recuperate at home.

[25] On September 2, 1862, Abbott's regiment covered the retreat of the defeated forces of Union Major General John Pope after the Second Battle of Manassas or Bull Run.

[24] Abbott missed the Battle of Antietam because he was hospitalized with typhoid fever and grief over the death of his brother at Cedar Mountain.

[35] Abbott in large part blamed Republican political leadership for the losses because they had removed Major General George McClellan, a fellow Democrat, from command of the Army of the Potomac.

[37] Major General John Sedgwick, commander of the "grand division" of which the 20th Massachusetts Infantry was a part, was ordered to take Fredericksburg and then come to the aid of the bulk of the Union Army which came under heavy attack from Confederate forces at Chancellorsville.

[41] The Confederate bombardment of Union positions on Cemetery Ridge at Gettysburg on the afternoon of July 3, 1863 was generally high and beyond the front line although the 20th Massachusetts Infantry Regiment did suffer a few casualties during the shelling.

[44] Then, Abbott had his men turn to help beat off the Confederate attack on the Union line at the copse of trees, which was at the very heart of the battle (the high water mark of the Confederacy).

[44] After Major General Meade demonstrated against Confederate forces at the battle of Mine Run Creek, the Army of the Potomac went into winter quarters at Brandy Station, Virginia.

[45] In December 1863, Abbott received a 15-day leave to visit home, which was extended by 20 days due to his suffering from chronic diarrhea.

[46] On May 4, 1864, newly appointed General-in-Chief of the Union Armies and Lieutenant General Ulysses S. Grant began his drive south into Virginia that became known as the Overland Campaign.

[50] Henry Livermore Abbott's service and exploits had gained him some notoriety so news of his death was met with consternation and grief at the highest levels of command and back in Lowell, Massachusetts.

"[26] On December 12, 1864, President Abraham Lincoln nominated Major Abbott for the award of the honorary grade of brevet brigadier general, United States Volunteers, to rank from August 1, 1864.

"[8] Major General Winfield Scott Hancock said "his reputation was built upon a solid foundation, and the closest scrutiny could not diminish it.

[54] Henry Livermore Abbott's good friend, future United States Supreme Court Justice Oliver Wendell Holmes Jr., who served in the 20th Massachusetts Volunteer Infantry Regiment with him, deeply admired Abbott for his courage and unruffled calm, and for his determination to do his duty even though he was deeply skeptical of Union war aims (except for preservation of the Union), was politically opposed to President Lincoln, and did not support the abolition of slavery because he thought it would die out in the near future.

Holmes considered Abbott an ideal soldier, and praised him in a famous 1884 Memorial Day speech stating that: "In action he was sublime.