There had always been patriots who wanted a Jerusalem independent from Rome, but after the year 60 a group of them became brutal. Back then there were no explosives for roadside bombings, but those terrorists did the next most lethal thing.
They armed themselves with short easily-hidden daggers called sheekas, and they themselves came to be called the Sheekari.
After ambushing every Roman patrol that took to the roads, the Sheekaris returned to their hiding places in Jerusalem. With all else failing, the Roman Senate ordered General Titus to destroy Jerusalem. The soldiers cut off all the roads and water lines, and set up catapults to fling fire balls into the city.
The Pharisees, who had always been business dealers with Romans, were allowed to leave the city, and they were faced with the task of keeping their religion alive. For that they decided that to be truly Jewish people had to keep all the precepts of the Law. That turned them against the Christians who would not avoid eatiing with Gentiles.