George Sykes got the boot after performing in a mediocre fashion in the fall campaign of 1863. Certainly, Warren's complaints about Sykes in the Bristoe Station Campaign had some impact. In Warren's estimation, Sykes and his V corps left Warren out to dry, and Warren felt that II Corps could have been destroyed by Lee's army.
And it was not without truth. Sykes was supposed to wait for Warren at Bristoe Station as Lee's army threatened to fall on the isolated corps. Instead, Sykes was moving off to Manassas despite his rear elements coming under Southern artillery fire. Despite the bombardment and sounds of battle, Sykes made no effort to turn around and even sent a fairly tone deaf message to Warren, telling him to hurry up or the full force of the enemy will come down on him as Warren's men were fighting for their lives against A.P. Hill's Corps + Allegheny Johnson's Division. Sykes only turned around when Warren made a direct request for help and Meade directly ordered him to turn around and help Warren. Sykes had an established reputation for being a slow commander, and this only cemented that reputation, especially when it was his word against a rising star in the Army of the Potomac.
As for Warren himself, I confess to be no fan of him. There were times when Warren was right, but Warren had too much of an ego and was open about his opinions on his peers. He even wrote a 12-page letter to A.A. Humphreys about how he would run a campaign if he were in charge, and how the army was being held back by certain officers. And then Warren fumbled badly in the Wilderness and Spotsylvania Court House battles. He had some good moments as in Globe Tavern and Bristoe Station, but it's hard to work with a subordinate who tries to second guess every single order received.
Bringing the