[DoodleDawg]

At the beginning of the War Between the States (Civil War) he was offered command of the U.S. Army by Abraham Lincoln. He knew that Lincoln’s invasion of the Southern States was unconstitutional, illegal, immoral, and criminal.

How could Lee know that, considering on April 18 Lincoln hadn't invaded anything?

[X Fretensis]

On April the 15th Lincoln called for 75,000 volunteers to put down the rebellion among Southern States. I suspect Colonel Lee surmised,from this action, that President Lincoln intended to attack those states that had seceded.