Changing the voting system in America will have little effect on the party system. However, the adoption of non-partisan runoffs like in Louisiana and Californi

Changing the voting system in America will have little effect on the party system. However, the adoption of non-partisan runoffs like in Louisiana and California will have a great effect on the people who are chosen. The current duopoly exists despite the voting system. Look at Canada and the UK, which have thriving national third parties and regional additional parites. And consider that NZ switched to MMP and Australia switched to IRV because of third party upsets. Canadians don't really worry if a vote for the NDP is a wasted vote - they vote NDP, and maybe their candidate gets up or maybe not. The duopoly exists because various states basically have laws requiring it - granting special privileges like ballot access or membership of the state gerrymandering commission to the too two parties. There may also be a contribution from the fact that electoral districts have vastly too many voters. Non-partisan runoffs increase the chances of a meaningful choice on voting day. IRV merely lets you vote for someone who won't get in. NPRV won't change the duopoly because that's required by law. But if you get a choice between the moderate Strawberry Pie party candidate and the extreme Strawberry Pie party candidate, you can get a good result from that.