American Civil War Union Army Major General. The son of wealthy Irish-American parents, he was orphaned when he was young, and was consequently raised by his maternal grandfather. Originally intent on becoming a lawyer at his grandfather's advice, he attended Columbia College in New York City and received a law degree in 1833. Three years later, his grandfather died and he inherited a fortune of over $1 million dollars. He then chose to make the army his profession and in 1837 he obtained a commission as a second lieutenant of cavalry and was assigned to the 1st U.S. Dragoons, who were commanded by his uncle, Colonel Stephen W. Kearny. In 1839 he was sent to France to study cavalry tactics, first attending school at the famous cavalry school in Saumur. He participated in several combat engagements with the Chasseurs d'Afrique in Algiers. The following year, he returned to the US and authored a cavalry manual for the Army based on his experiences with the French military. He has a few stateside assignments until 1846, when the US declared war on Mexico. He became the personal bodyguard of General Winfield Scott. He led his men in the battles of Contreras and Churubusco; in the latter engagement, he led a daring cavalry charge and suffered a grapeshot wound to his left arm which had to be amputated. In 1851 he was a member of a unit that saw action against the Rogue River Native American tribe in Oregon. He resigned his commission later that year and embarked on a trip around the world, visiting China, Ceylon, and France. In 1859 he returned to France, re-joining the Chasseurs d'Afrique, who were at the time fighting against Austrian forces during the Second Italian War for Independence. Later, he was with Napoleon III's Imperial Guard at the Battle of Solferino, where he charged with the cavalry under General Louis-Michel Morris, which penetrated the Austrian center and captured the key point of the battle. For this action, he was awarded the French Légion d'honneur, becoming the first US citizen to be thus honored. When the American Civil War broke out in 1861, he returned to the US and was appointed a brigadier general, commanding the 1st New Jersey Brigade. In April 1862 he received command of the 3rd Division of the III Corps and led it into action at the Battle of Williamsburg, the Battle of Fair Oaks, and the Battle of Malvern Hill. After the Union forces were routed at the 2nd Battle of Bull Run in August 1862, in which he participated, he was killed at the Battle of Chantilly upon stumbling into a Confederate line and refusing to surrender. His body was forwarded to the Union line by Confederate General Robert E. Lee under a flag of truce, and his death was lamented by commanders on both sides. His body lay in an unmarked vault in Manhattan's Trinity Churchyard until 1912, when the efforts of Congressional Medal of Honor recipient Charles Hopkins (who had served under General Kearny in the First Jersey Brigade) secured his re-burial with full military honors in Arlington National Cemetery.