Three Reasons minor parties form

Answer 1

They don't believe either major party's candidate is fulfilling certain needs, they have a certain disagreement with one of the major parties (splinter party), or they're taking a stronger stand on a specific issue (single-issue party).

Answer 2

The primary purpose of third-party candidates running for public office is to call attention to otherwise ignored, misrepresented, or even suppressed principles or issues.

The secondary purpose is to get the major parties to adopt the most important portions of the 3rd party platform as part of theirs.

Answer 3

I see two important roles for minor parties. First, they may popularize ideas which will later be adopted by more major parties. And secondly, every party has to start somewhere; minor parties may eventually become major parties.