At the end of the war, President Andrew Johnson offered amnesty to the overwhelming majority of Confederate soldiers. The sweeping offer did not, however, apply to all. Johnson's Amnesty Proclamation excepted high ranking civil and military officials, as well as those in possession of large estates (exceeding a value of $20,000). These individuals had to apply for a pardon - and had to do so personally to the president.
As did James Longstreet. But it really helps when the commander of the Union armies writes you a letter of reference. Ulysses S. Grant and James Longstreet were pals in the old army, and he clearly admired him. And what do you know...Old Pete was, shall we say, Republican friendly. He even supported Grant for president in 1868. Now how many former Confederates do you think did that? (hint: not many).
Here is what Sam Grant had to say about his old friend:
His EXCELLENCY A. JOHNSON,
Knowing that General Longstreet late of the army which was in rebellion against the authority of the United States, is in the city, and presuming that he intends asking executive clemency before leaving, I beg to say a word in his favor.
General Longstreet comes under the third, fifth, and eighth exceptions made in your proclamation of the 29th of May, 1865. I believe I can safely say that there is nowhere among the exceptions a more honorable class of men than those embraced in the fifth and eighth of these, nor a class that will more faithfully observe any obligation which they may take upon themselves.
General Longstreet, in my opinion, stands high among this class. I have known him well for more than twenty-six years, first as a cadet at West Point and afterwards as an officer of the army. For five years from my graduation we served together, a portion of the time in the same regiment. I speak of him, therefore, from actual personal acquaintance.
In the late rebellion, I think, not one single charge was ever brought against General Longstreet for persecution of prisoners of war or of persons for their political opinions. If such charges were ever made, I never heard them. I have no hesitation, therefore, in recommending General Longstreet to your Excellency for pardon. I will further state that my opinion of him is such that I shall feel it as a personal favor to myself if this pardon is granted.
Very respectfully, your obedient servant,
U. S. GRANT,
I'll bet Grant got a Christmas card from Casa Longstreet every year.