He was in command in May, 1861, at Fortress Monroe, and he found that when fugitive slaves sought the protection of his camp they were pursued under flags of truce, and their return was requested as a right under the Constitution of the United States by men who were in arms against the Constitution.
The anomaly of this situation was seen by General Butler, and he met it promptly by refusing to permit the slaves to be returned, declaring them to be contraband of war.

As they were useful to the enemy in military operations, they were to be classed with arms and ammunition.

This opinion was at first received joyously by the country, and the word "contraband" became the synonym of fugitive slave.

But General Butler's judgment is justified by the rules of modern warfare, and its application solved a question of policy which otherwise might have been fraught with serious difficulty.
In the presence of arms the Fugitive-slave Law became null and void, and the Dred Scott decision was trampled under the iron hoof of war.
SLAVERY ABOLISHED IN THE DISTRICT.
The first exercise of legislative power hostile to the institution of slavery, already detailed, was promptly followed by one still more decisive.

Congress provided for the abolition of the institution in the District of Columbia.