There are a number of systems through which elections are carried out and also how governments operate. These include the majority system, the proportional representative system as well as the presidential, parliamentary, unitary and federal government.
A unitary system is composed of one central government that holds all the power, but a federal system divides power between national and local forms of government. Many unitary governments are either dictatorships or totalitarian. On the other hand, power is decentralized in the federal government.
A country with a unitary or federal system of government can choose to adopt the one-party, two-party or multi-party system. However, some choices are more likely than others. For instance, a unitary system is more likely to adopt a one-party system.
A one-party state is a form of government where the country is ruled by a single political party, meaning only one political party exists and the forming of other political parties is forbidden.
Some countries have many political parties that exist, but only one that can by law be in control, which is called a one-party dominant state. In this case opposition parties against the dominant ruling party are allowed, but have no real chance of gaining power.
A multiparty system, on the other hand, is one where multiple political parties exist and have a chance of leading the government. In other words, the parties all compete to win an election to govern the state. This system is quite different from the United States where there are two political parties that dominate the political field. These are the Republican and Democratic political parties. Examples of countries that have a multiparty political system are Canada, which has six political parties, and Nigeria, which has 68 registered political parties.