When do political parties split? Answer lies in diverging voter interests

When voter interests diverge, parties split. If space allows, both survive. If not, only one remains

Why do political parties split — or stay together? For most of us, the obvious and intuitive approach to party politics is the following: Parties represent a relatively cohesive bloc of voters who are aligned by material interest, or regional or community consciousness, or economic ideology. When the interests of some of these voters diverge from others, then parties split. If there is space in the polity for an additional party, then both survive. Otherwise, only one does.

The British parliamentary system, the ancestor of most other legislatures, demonstrates this quite effectively. There is space for two