In one-party systems, one political party is legally allowed to hold effective power. Although minor parties may sometimes be allowed, they are legally required to accept the leadership of the dominant party. This party may not always be identical to the government, although sometimes positions within the party may in fact be more important than positions within the government. North Korea and China are examples; others can be found in Fascist states, such as Nazi Germany between 1934 and 1945. The one-party system is thus usually equated with dictatorships and tyranny.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): When was Nazi Germany in a one-party system?
1934 and 1945