Some other theories relevant to this: https://en.wikipedia.org/wiki/Duverger%27s_law https://en.wikipedia.org/wiki/Duverger%27s_law https://en.wikipedia.org/w

Some other theories relevant to this: https://en.wikipedia.org/wiki/Duverger%27s_law https://en.wikipedia.org/wiki/Duverger%27s_law https://en.wikipedia.org/wiki/Median_voter_theorem https://en.wikipedia.org/wiki/Median_voter_theorem https://en.wikipedia.org/wiki/Realigning_election https://en.wikipedia.org/wiki/Realigning_election (events where party political coalitions do fracture, despite efforts to keep them together)