A city-state is a region controlled exclusively by a city, and usually having sovereignty. Historically, city-states have often been part of larger cultural areas, as in the city-states of ancient Greece and Phoenicia, the Aztecs and Mayans of pre-Columbian Mesoamerica, along the Silk Road in Central Asia, or the city-states of Renaissance Italy.
City-states were common in ancient times. Though sovereign, many such cities joined in formal or informal leagues under a high king. In some cases historical empires or leagues were formed by the right of conquest (e.g., Mycenae, or Rome), but many were formed under peaceful alliances or for mutual protection (e.g., the Peloponnesian League).
In the Middle Ages, city-states were particularly a feature of what are now Germany, Italy and Russia. A number of them formed the Hanseatic League, which was a significant force in trade for a number of centuries.