After Dinah was abducted by Shechem, his father, Chamor, came to Yaakov and his sons and requested that they allow his son to marry Dinah. Yaakov's sons responded that it would be a disgrace for them to give their sister to an uncircumcised man. Therefore, only if every male in the city would circumcise himself would Bnei Yisrael give their daughters to the people of Shechem and likewise marry their daughters. Chamor and Shechem agreed at once and they also succeeded in convincing the rest of the citizens of their town to follow suit.
On the third day after their circumcision, Shimon and Levi entered the city of Shechem and killed every male, and took their sister Dinah and left. The Torah relates Yaakov's response to Shimon and Levi's actions: "You have sullied me, making me disgusting among the inhabitants of the land, and I am few in number, and should they band together and attack me they will destroy me and my household" (Bereishis 34, 30). To which they retorted, "Should our sister be treated like a harlot?"
The question begs to be asked: What type of answer was this? Yaakov was understandably worried for the safety of his family and they seemingly totally disregarded this concern. Rav Wolbe (Shiurei Chumash) explains their response as follows. The very essence of Bnei Yisrael is associated with the fact that they are, "A nation that dwells in solitude" (Bamidbar 23, 9). They cannot assimilate with the other nations of the world and the abduction of Dinah was the first instance where the other nations attempted to mingle with Bnei Yisrael and their daughters. Shimon and Levi's answer to Yaakov was that it is completely unacceptable to abandon a Jewish girl and let her live with a gentile. They could not remain silent in face of what had occurred, and annihilating the city was worthwhile even if their actions would cost them their lives!
The above was the first time that there was an attempt to cause Jews to merge with non-Jews, but certainly not the last time. The story of Chanukah was another such attempt made by the Greeks and Hellenists alike. Once again, the leaders of Bnei Yisrael decided that they would not remain silent to the situation at hand - even if it would cost them their lives! A handful of tzaddikim risked their lives to fight the mighty Greek army, and Hashem responded to the efforts of these righteous men and granted them a miraculous victory. Yiddishkeit does not allow for any assimilation with the non Jewish nations to the extent that it is worthwhile for us to give up our lives rather than forfeiting our ability to "dwell in solitude!"