<human>:  Why did the Union lose at the Battle of Chancellorsville?
<bot>: The Union lost because the Confederate army had superior tactics. They had more men and more guns, and they were better organized. The Union army was not well trained and had a lot of trouble coordinating their movements. The Union army was also poorly supplied and was not able to bring in enough supplies to feed their soldiers. The Confederates also had more generals who were better at commanding the army.