After general mcclellan was replaced by general burnside, union forces

After McClellan did not follow General Robert E. Lee after the Battle of Antietam, Burnside was named general of the Potomac Army on November 10, 1862, replacing McClellan. Burnside decided to try a quick approach to Richmond, provoking on December 13 the Battle of Fredericksburg, during which the Union Army received a severe defeat. In the face of this debacle of the Union, combined with a second failed attempt that would be known as the "Mud March", was relieved of command, being replaced by General Joseph Hoker at the head of the Army of the Potomac.

d.prevent the spread of communism outside of eastern europe.