Many define terrorism based on their opinions, not on reason.
That means a Palestinian killing an Israel soldier in occupied Palestine is a terrorist, but US B52s carpet bombing Cambodia was not.
If you attack unarmed civilians in order to force your opinions and ideals onto others, you're probably a terrorist.
Lets not forget that before the British escaped from Palestine, Jews were "terrorizing" them;
- Many Jews had fought for the Allies during WWII and had developed their military skills as a result. After the war ended in 1945, these skills were used in acts of terrorism. The new Labour Government of Britain had given the Jews hope that they would be given more rights in the area