Polity established as a centralised organisation is called state. There is no clear definition of state and as per Max Weber's definition state is a polity that maintains monopoly on the use of violence.
State can be sovereign and non sovereign. Sovereign state is the state where the supreme authority lied in the state itself, while non sovereign state's sovereignty lies in other states. It is also used for federated states such as USA in which the sovereignty is shared between a federal body and member states.
The first states about 5500 years ago with the rapid growth of cities and invention of writing and over time various forms of state developed and depended on variety of justification for their existence.
