A state is defined by multiple characteristics, including a government body and bureaucracy, a concentration of labor and population and a surplus of food. Other characteristics involve social stratification of the people and the levying of taxes for public works, military and police forces.
Sovereign states are those that require no outside powers to provide these characteristics, as they can generate these resources from within their borders. Federated states give up portions of their power to a federal government designed to harness the economic strengths of the states as a whole. A state's power is in constant flux due to changes in political, economic and military policies. States rely on rule of law to alter many of these characteristics, and they require governments to enforce these laws.
Both nations and governments differ from the definition of a state. Nations are defined as a geographical region and the people who share the area as one social group, whereas a government is the group of people that controls the mechanisms of state maintenance. While the three concepts often intertwine, each defines a different portion of the group of people or area. Some of the earliest historical examples of states are Rome and Greece.