Two-party system
A two-party system is a party system where two major political parties dominate the government. One of the two parties typically holds a majority in the legislature and is usually referred to as the "majority" or "governing party" while the other is the "minority" or "opposition party". Around the world, the term has different senses. For example, in the United States, Jamaica, and Malta, the sense of "two-party system" describes an arrangement in which all or nearly all elected officials belong to one of the only two major parties, and third parties rarely win any seats in the legislature. In such arrangements, two-party systems are thought to result from various factors like winner-takes-all election rules. In such systems, while chances for third-party candidates winning election to major national office are remote, it is possible for groups within the larger parties, or in opposition to one or both of them, to exert influence on the two major parties. In contrast, in the United Kingdom and Australia and in other parliamentary systems and elsewhere, the term "two-party system" is sometimes used to indicate an arrangement in which two major parties dominate elections but in which there are viable third parties which do win seats in the legislature, and in which the two major parties exert proportionately greater influence than their percentage of votes would suggest.
Plurality voting
The countries that inherited the British majoritarian system tend toward two large parties: one left, the other right, such as the U.S. Democrats and Republicans. Canada is an exception, with three major political parties consisting of the New Democratic Party which is to the left, the Conservative Party which is to the right and the Liberal Party which is slightly off center to the left. A fourth party that no longer has major party status is the separatist Bloc Québécois party, which is territorial and concentrated in Quebec. New Zealand used the British system, and it too yielded two large parties. It also left many New Zealanders unhappy, because other viewpoints were ignored, so its parliament in 1993 adopted a new electoral law, modelled on Germany's system of proportional representation (PR) with a partial selection by constituencies. New Zealand soon developed a more complex party system.