 Portions of northwestern Mississippi were under Union control on January 1, 1863, when the Emancipation Proclamation went into effect.All of Mississippi had been declared "in rebellion" in the Proclamation, and Union forces accordingly began to free slaves in the U.S.-controlled areas of Mississippi at once.According to one Confederate lieutenant from Mississippi, slavery was the cause for which the state declared secession from the Union, saying that "This country without slave labor would be completely worthless ... We can only live & exist by that species of labor