A fundamental principle of a republican form of government is that

The fundamental principle of a Republic form of government is the separation of different government bodies and the limits of power on the head of State.

Explanation:

In effect, this means that the government and the country are 'public matters' and not the affair of a few unelected head of States.

The basic idea is to give power back to the people and ensure that the country is run by the many and not the few.

The ideals of Republican government are not new and have existed in some form since the ancient Roman Republics.

Today, most countries describe themselves as Republics, though, it is a matter of dispute if they are truly are one.