The battle of fort sumter why did they not shoot back?

The US Army refused to fire on the Southern troops. Probably because of all the bloodshed that already happened, thus they surrendered.

1. The Battle of Fort Sumter was the bombardment of Fort Sumter near Charleston, South Carolina by the Confederate States Army, and the return gunfire and subsequent surrender by the United States Army that started the American Civil War. Wikipedia;

2. The Battle of Fort Sumter (April 12–13, 1861) was the bombardment of Fort Sumter near Charleston, South Carolina, by the Confederate States Army, and the return gunfire and subsequent surrender by the United States Army that started the American Civil War.

3. Battle Summary: Fort Sumter, SC. Description: On April 10, 1861, Brig. Gen.Beauregard, in command of the provisional Confederate forces at Charleston, South Carolina, demanded the surrender of the Union garrison of Fort Sumter in Charleston Harbor. Garrison commander Anderson refused.