Our country, for the most part, has always voted off a two party system. Every party besides the Democrats and Republicans, each representing important issues, never get the chance to address those said issues. For example, the green party doesn't have a chance to get their message across with the current system.
A Two-round system would give these minority parties some power. The way it works is that the winner MUST have an absolute majority. After the first election, if no one has met the qualifications, those minor parties can throw their backing to the bigger parties in exchange for them to recognize the issues. A second election is then held and whomever wins will have to pay attention to the other issues. This would truely give every American a voice.