What issue divided shiite and sunni muslims?

Read this excerpt from the call of the wild by jack london. the encouragement buck gave the rebels led them into all kinds of petty misdemeanors. no more was spitz a leader greatly to be feared. the old awe departed, and they grew equal to challenging his authority. pike robbed him of half a fish one night, and gulped it down under the protection of buck. another night dub and joe fought spitz and made him forego the punishment they deserved. and even billee, the good-natured, was less good-natured, and whined not half so placatingly as in former days. buck never came near spitz without snarling and bristling menacingly. in fact, his conduct approached that of a bully, and he was given to swaggering up and down before spitz's very nose. who is the antagonist in this excerpt? buck is the antagonist because he has started a rebellion. spitz is the antagonist because the others are rebelling against his leadership. dub and joe are the antagonists because they attack spitz. billee is the antagonist because he refuses to cooperate with the others.