During the First Crusade, Christian knights from Europe capture Jerusalem after seven weeks of siege and begin massacring the city's Muslim and Jewish population.
Explanation:
... In June, the crusaders captured the Turkish-held city of Nicaea and then defeated a massive army of Seljuk Turks at Dorylaeum.
It warned Roosevelt that Germany was developing an atomic bomb and encouraged him to start a nuclear program in the US that later became the Manhattan Project
