Assassins Order in History?

I am a fan of the video game assassins creed, I am told it is based on real history, So i am wondering if there is any info or history of this secret assassin order there is history on the templars so hopefully there is info on the assassins thank you
The Assassins were an Ismaili sect based in the castle of Alamut in the Elburz Mountains. They did use assassination as an instrument of policy. Bernard Lewis wrote a book called The Assassins - A Radical Sect in Islam



http://en.wikipedia.org/wiki/Hashshashin
The crusades were to protect people to get to Jerusalem without getting killed by radicals in the areas they had to cross. There were no such things as assassins. It was made up to have a good plotline.
Game designers take a lot of artistic liberty with