What is the justification of the state? Or to put it differently: From what source does the legitimate authority of any particular government arise?
There is a loose sense of the word "state" in which all the citizens of a particular territory are part of the state -- in the sense in which we are all part of the United States. In that sense, "state" means something like "country." But as the term is usually used in philosophy, "state" has a more restricted meaning; it means, basically, the government.
The state, or government, is not some totally monolithic "leviathan" (to use Thomas Hobbes's term), a single entity with a single mind and a single will -- even though words like "the state" and "the government" , may invite us to think of it that way. The state is made up of people (such as the president), some items at their disposal or so-called public property (such as government buildings and weapons), and particular habits or traditions (such as those things that are called "laws").
One kind of justification is epistemic justification-- the sort of justification that some of our beliefs have. When we talk about the justification of the state, we're talking about justification in a different sense -- in a moral sense of the word. If a state is "justified" in this moral sense of the word, then it is, as we say, legitimate. It is a legitimate government; and it has a moral right to rule.
What exactly are we talking about when we ask about the moral justification of the state? Are we asking for the moral justification of the existence of particular politicians, or particular government buildings, or particular laws? The question isn't about any one particular government; it's about an aspect of any government: the monopoly on the legitimate initiation of force. How are the people in any government morally justified in engaging in any practice that involves threatening or using force?
If they couldn't use force, there would be no government. Distinguish two senses of this question. Like this:
For example, it's the threat of force that keeps people paying taxes, and it's taxes that keep the government running at all. So: no tax enforcement, no government. It's easy to forget this, but it's true.
Focus on (1), rather than (2). Ask why the state should exist at all -- why the power of government agents to initiate force should be thought to be morally legitimate.