Minecraft wiki entry for Building_a_metropolis, associated text: Marxist-Democracy
The common people hold most of the power. They propose and vote on all the laws, decide what the resources are used for, and can declare war on other countries.
There is an executive branch of the government that contains a president. The president is essentially a figurehead that meets with leaders from other countries and represents the nation as a whole. They are elected by a popular vote and can also be impeached by the citizens as well. The of power the president holds is that they can veto the laws that are passed by the people; however, the people can override the veto.
Every member of the country is trained in combat and serve in the military. When in times of war, one person is put in control of the military and who is elected in the same from as the president.
There also is a constitution that lays out the ground rules that the nation will follow. It can include presidenial term limits, what percent of the people are needed to override a veto, etc...
The economy is based off communism with the people holding specific jobs and working for the good of the entire nation. All materials are collected and held in a government storage facility. People that do not work could have their voting rights taken away, be thrown in jail, or whatever the constitution/laws decide.
This form of government works best within a city-state or the same group of people that can be all of the same mindset (to avoid revolutions).