the united states of america currently operates elections with something called ‘first past the post voting’. aka Winner Takes All.
the Alternative Vote, on the other hand, is a mathematically superior process that significantly reduces the chance of ending up with a two party system. by ranking candidates, election results more closely reflect the choice of the voters, which in turn helps guard against minority rule and means no spoiler effect.
the spoiler effect is how a third party influences an election, where that party is know as the ‘spoiler’ because it can take votes away from one of the major candidates (presumably the one with somewhat similar views) often leading to a victory for the major candidate with the most dissimilar platform.
for an explanation on First Past the Post Voting, and how it evolves check out this video