When Haman convinced King Ahashverosh to issue a decree allowing the people to attack and plunder the Jews, it says nothing about not allowing the Jews to defend themselves. Yet near the end of the megilla, after Esther and Mordechai issue a new decree that Jews should defend themselves (because they could not repeal the previous decree), the Megilla relates the joy among the Jews that they could defend themselves, and how they gathered together to fight against the attackers and how nations feared the Jews because of their right to defend.
Pretty amazing the metamorphasis the jews went through. They were about to be slaughtered and obviously felt they could not defend themselves. they would have gone like sheep to the slaughter, excuse the terminology. Yet suddenly they have a boost of confidence. Suddenly they are defending themselves and valiantly at that! The goyim are afraid of the Jews!! Amazing! The goyim were about to walk over the Jews with no problem, and suddenly the tables have turned.
All it takes is some confidence and a change of attitude.