Sea power, classically defined as a strategy to control communications, was an essential asset for the creation of European maritime empires, enabling them to secure seaborne trade, open new markets, and acquire territory. It has often been conflated with seapower, a concept developed by the ancient Athenians to distinguish states like their own, whose economy, culture, and identity were enmeshed in the maritime sphere, from continental military powers like Sparta and Persia. In this period Britain, the only seapower Great Power, created an extensive maritime empire outside Europe, one combining colonies of settlement, like Australia, with those of occupation, and informal imperialism based on economic power. While many Continental European powers created maritime empires after 1815, they did so in the knowledge that their possessions would be exposed to British naval power in the event of war, and tended to focus on land and security rather than commerce.