Because Uthman has a fellow member of the Umayyad clan, the Umayyad clan, they're also Quraysh, just like Muhammad's clan, the Hashem, are also Quraysh, and Uthman's family member, Muawiyah, has been governor of Damascus since the time of the caliph, Umar. And when Uthman is assassinated, Muawiyah is not happy. And when Ali comes to power, he thinks that Ali is not making a solid effort to put the assassins to justice, and he refuses to pledge his allegiance to Ali as the caliph. Now the other context here is that Muawiyah has already built a significant military force, and that force is becoming stronger and stronger and stronger. And so this leads to a lot of tension. Muawiyah wants Ali to bring the assassins of Uthman to justice, and Ali wants Muawiyah to pledge allegiance to him, who is now caliph. Now just for a little bit extra context, Ali also decides to move the capital of the caliphate to Kufa, which is in modern-day Iraq.