The vicksburg Campaign convinced Lincoln that Grant was the right man to lead the whole Union Army.
Shorter and less deadly.
Abraham Lincoln died, the Union had another victory, and the slaves were freed.
John Wikes Booth assassinated President Lincoln in hopes of disrupting Union military tactics, as well as eliminating the possibility of the "Lincoln dynasty" in the words of Booth. He was concerned (as were many others) that Lincoln's tight association with the military and his tendency to act without or against the consent of congress may lead to a tyrannical takeover.
After the Union defeat at the First Battle of Bull Run, President Lincoln called Major General George B. McClellan to come to Washington DC and organize the Union army there into a well organized fighting force. Later, after the Union defeat at the Second Battle of Bull Run under Major General Pope, McClellan was again asked to command Union armies in the East. Pope had failed and McClellan was put in charge again of the Army of the Potomac. He would again have to deal with the Army of Northern Virginia under the command of Lieutenant General Robert E. Lee.
After the liberation of the Mississippi, Grant was ordered East, to rescue the Army of the Cumberland from starvation at Chattanooga.
After McDowell's failure at the First Battle of Bull Run, George McClellan was ordered to lead he Union army in the east. This was order was given by Lincoln.
Henry Wirz
George Brinton McClellan.
The Union Army had several leaders. Some of them were George McClellan, William Tecumseh Sherman, and Ulysses S. Grant. Abraham Lincoln was President during the Civil War.
The vicksburg Campaign convinced Lincoln that Grant was the right man to lead the whole Union Army.
Shorter and less deadly.
Hooker, Meade, and Grant.
Abraham Lincoln
If the question pertains to the US Army of the Potomac, the last general to lead all the Union armed forces was Ulysses S. Grant. He was appointed by Lincoln and only reported to Lincoln. Whom ever might be leading any part of the Army of the Potomac, they reported to Grant. Grant was the last of a long line of generals to be appointed to lead all the Union forces.
Santa clasue
Following the Union defeat at Fredericksburg in December 1862, President Lincoln replaced General Ambrose Burnside with General Joseph Hooker. Hooker was appointed to lead the Army of the Potomac, and he was tasked with revitalizing the Union forces and improving their strategic effectiveness in the ongoing Civil War. Lincoln hoped that Hooker's leadership would reinvigorate the army after the significant losses at Fredericksburg.