Why isn't there a third major political party besides the Republicans and the Democrats?
The upper classes split over politics back in the early 1800's, and have kept it that way for most of the years since. Most states let the Party that won the last election cycle control the ballot boxes and voting rules for the next election, and part of that includes using fake lawsuits challenging 'third party' petitions to be placed on ballots; both parties do this, which is why even if you're well known and famous, like a Ralph Nader, you will be blocked from being on the ballot in many states, as your party doesn't have the money to fight endless legal challenges over signatures, while the two big Parties have endless resources to do so, same as big companies like Apple and Intel can harass smaller companies with endless bogus patent infringement lawsuits into selling out cheap or going bankrupt.