When Mohammed first came to Medina he was politically weak and forged an alliance with the Jewish tribes there in the form of a pact of mutual defence and nonaggression. After a while he began to attack the trade caravans of the Meccans and aggressively provoke them to instigate a war. Mohammed was the clear aggressor and the Jews of Medina saw this. His actions were not necessary to defend himself. They were purely aggressive in nature with the goal of attaining complete political and religious dominance over a tribe which only sought to trade to make a living peacefully without violence and practice its own religion. The Meccans never attacked Mohammed outside Mecca. Mohammed constantly sought to prevent the Meccans from practising their religion in and around the Kaaba and take control of the Kaaba himself. Mohammed was also threatening the Jews because they did not believe his claim to be a prophet. So we see that neither the Meccans nor the Jews were actually using violence or even threatening to use violence against Mohammed. He was the one that was threatening the Jews with violence if they did not become Muslims and attacking the trade caravans of the Meccans. In this situation the Jews were forced to revoke their treaty with Mohammed and seek for a way to defend themselves against his aggression. The only avenue left to them was to try to remain neutral or seek protection from Mohammed from the only group that had the means to defend themselves against his aggression. For this reason Mohammed unjustly attacked the Jews of Medina by exiling, robbing, enslaving and killing them in the same way as the warners and messengers who are described in the Koran as his predecessors. All you will hear from Muslim apologists is that the Jews broke their treaty but they will not tell you why.