How did rule differ under oligarchies, democracies, and republics?

Oligarchies are a form of government where a small group of people have control over a country. These forms of government are usually oppressive and can lead to corruption.

Democracies are a form of government where the whole population of the country decides the course of actions and its laws. This would be the rule of the majority. This form of governing usually doesn't have corruption and the majority rule. These can, however, have negative effects. If the country isn't educated properly, then they aren't going to be making responsible decisions for their country. 

Republics are the biggest forms of government currently. It is a where supreme power is held by the people and their elected officials. Usually, the elected officials have more say on laws and policies. These can tend to see corruption either big or small from time to time.