Remember that on the 13th of Adar, Jews across the kingdom assembled and, before the Babylonians could attack, the Jews attacked and killed thousands of the Babylonians, including Haman's 10 evil sons who were hanged from a tree.

This was also allowed by the God of the Jews and was probably the first story of a "pre-emptive strike."

The Old Testament has several instances of "hey, we believe that those people are going to destroy us Jews, so we will destroy them to protect ourselves."