Lee at that time was considered the best general in the U.S. army.
Pres. Lincoln even offered Lee command of the entire Union army.
Lee rejected the offer because he was from the southern state of Virginia and took command of the Confederate army.
Even today, Gen. Lee's battlefield tactics are taught and studied at West Point and other military schools around the world. ...
Sort of. A time line helps.
April 15 Lincoln calls for 75000 troops to be raised by governors to put down the rebellion in the cotton states.
April 17 In response to this act, found repugnant to those believing the union to be a voluntary organisation, Virginia secedes.
April 18 Lee is offered command. Recognizing that the coming war would be largely fought in Virginia, Lee declines the offer.
April 20 Lee resigns his commission in the union army. He pens a letter to General Winfield Scott concluding with “Save in the defense of my native State, I never desire again to draw my sword.”
April 22 Lee is appointed commander of the defenses of Virginia.