An empire is a set of lands, regions or countries that are ruled by an Emperor. An empire usually also has many different cultures. In history, many empires were usually formed when a country began to invade or colonise nearby countries.
Usually, an empire is ruled by one dominant country. For example, the British Empire was largely controlled by the United Kingdom's government.
Well-known empires include the Persian Empire, Roman Empire, Russian Empire, Greek Macedonian Empire, Holy Roman Empire and British Empire.