2-party system, and no third party has ever actually posed a threat and survived more than an election cycle without replacing one of the pre-existing two parties accordingly. We simply don't have a system that caters to multiple parties because our legislature is designed to be representative with majority rule. If we wanted to have 4-5 viable parties that all have influence we would have gone the route of a parliamentary system. We did not, and your point is 100% invalid accordingly.