As Greek city-states become more and more populous, and affluent, their societies began to find new ways to expand. With Athens being one of the more dominant city-states, it expanded outwards across its nearby seas. It developed a powerful navy and colonized many islands in the Greek Archipelago and Asia minor. The city states valued the opinions of the people who lived in them, as long as they were Greeks. The idea of citizenship developed, as did arguably their most important concept, the idea of democracy.