From Halopedia, the Halo wiki

There is more information available on this subject at Democracy on the English Wikipedia.

Democracy is a form of government in which all people have an equal say in the decisions that affect their lives. A common feature of democratic governments, as currently understood and practiced, is competitive elections which require freedom of speech, freedom of the press, and rule of law. Civilian control of the military is often seen as necessary to prevent military interference with political affairs.[1] Democracy describes a small number of related forms of government and also an encompassing political philosophy. The word stems from the term "dēmokratiā" which was coined dēmos (“people”) and kratos (“rule”) in the middle of the 5th century BC to denote the political systems then existing in some Greek city-states, notably Athens. The government of the Greek city-state of Athens was the first to use the democratic system around the year 500 B.C.

The Unified Earth Government is based on a democratic governance, which controls its colonies and member nations on Earth as well as on other planets.[2]