One-party states explain themselves through various methods. Most often, proponents of a one-party state argue that the existence of separate parties runs counter to national unity. Others argue that the one party is the vanguard of the people, and therefore its right to rule cannot be legitimately questioned. The Soviet government argued that multiple parties represented the class struggle, which was absent in Soviet society, and so the Soviet Union only had one party, namely the Communist Party of the Soviet Union.
Some one-party states only outlaw opposition parties, while allowing allied parties to exist as part of a permanent coalition such as a popular front. However, these parties are largely or completely subservient to the ruling party and must accept the ruling party's monopoly of power as a condition of their existence. Examples of this are the People's Republic of China under the United Front, the National Front in former East Germany and the Democratic Front for the Reunification of the Fatherland in North Korea. Others may allow non-party members to run for legislative seats, as was the case with Taiwan's Tangwai movement in the 1970s and 1980s, as well as the elections in the former Soviet Union.
Within their own countries, dominant parties ruling over one-party states are often referred to simply as the Party. For example, in reference to the Soviet Union, the Party meant the Communist Party of the Soviet Union; in reference to the pre-1991 Republic of Zambia, it referred to the United National Independence Party.
Most one-party states have been ruled either by parties following the ideology of Marxism–Leninism and international solidarity (such as the Soviet Union for most of its existence), or by parties following some type of nationalist or fascist ideology (such as Italy under Benito Mussolini), or by parties that came to power in the wake of independence from colonial rule. One-party systems often arise from decolonization because one party has had an overwhelmingly dominant role in liberation or in independence struggles.
One-party states are usually considered to be authoritarian, to the extent that they are politically totalitarian. On the other hand, not all authoritarian or totalitarian states operate based on the one-party rule. But very few, especially absolute monarchies and certain military dictatorships, have no need for a ruling party, and they make all political parties illegal.