This question comes from a string below, that really was attached to a different subject, but I thought it would be a good topic. No disrespect to the originator of the question, I am pulling it out of his context to answer these words straight up.
Fort Pillow was a military position whose intent was to protect the northern approaches of the Mississippi River to Memphis, Tennessee. It was built by the Confederates, used successfully, until overwhelming Union forces out flanked the garrison forcing its evacuation early in the war. Off and on, the Union military used the position and garrisoned it with different units. By 1864, its strategic importance had long ago been changed by the war's events. General Sherman had directly ordered it's garrison removed and the fort abandoned weeks before the events for which it is famous. Since the fort came under the command of the Union officers in Memphis, they had disobeyed a direct order by their superior commander. Rumors and facts point to the post being used for illegal activity by the Union officers in Memphis. Most probably for the smuggling of contraband property and or stolen goods.
The question "what justified Fort Pillow" is meant to say that the Confederates had no justification for attacking Fort Pillow, no justification for killing a large part of the garrision, no justification for killing negro troops, no justification for killing men who were helpless and had surrendered. The truth, the complete facts, gives more weight to the probability that the Confederates actions were more justified than the existance and purpose of the Union garrison within the fort.
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David Upton