What causes increase of third party voting ?

[jman123]

What elements have to combine to cause an uptick in third party voting at gubernatorial,  senatorial, and presidential elections individually?

[darklordoftech]

Generally because there's an issue that neither of the main parties is addressing. For example, the Free Soil Party because neither party was addressing slavery.

[Adam Griffin]

Disdain for one or both major party candidates among their otherwise natural electorates. In the modern era, this is tied more to qualms over personality than ideology.

[Nyvin]

Also there can't be any "Us VS Them" mentality.    This explains why third parties do better in open presidential elections rather than ones with an incumbent running for re-election.