The initial Confederate response was one of expected outrage. The Proclamation was seen as vindication for the rebellion, and proof that Lincoln would have abolished slavery even if the states had remained in the Union. In an August 1863 letter to President Lincoln, U.S. Army general Ulysses S. Grant observed that the Proclamation, combined with the usage of black soldiers by the U.S. Army, profoundly angered the Confederacy, saying that "the emancipation of the Negro, is the heaviest blow yet given the Confederacy. The South rave a great deal about it and profess to be very angry." A few months after the Proclamation took effect, the Confederacy passed a law in May 1863 demanding "full and ample retaliation" against the U.S. for such measures. The Confederacy stated that the black U.S. soldiers captured while fighting against the Confederacy would be tried as slave insurrectionists in civil courts—a capital offense with automatic sentence of death. Less than a year after the law's passage, the Confederates massacred black U.S. soldiers at Fort Pillow.