--Look at countries that don't have the two party system, like Mexico during most of the 20th Century, the USSR, China, and Iran.--
Those are (or were in the USSR case) all ONE party states. Many of us believe that the US has become a de facto one party state; the one party having two wings called "republican" and "democrat."
Not two many countries have successful systems with more than two parties. Italy comes to mind as an example of a multiparty system (what is it, 50 governments in 50 years?).