Sri Lanka is a semi-presidential representative democratic republic, whereby the President of Sri Lanka is both head of state and head of government, and it relies on a multi-party system. Executive power is exercised by the President on the advice of the Prime Minister and the Cabinet of Ministers. Legislative power is vested in the Parliament. For decades, the party system was dominated by the socialist Sri Lanka Freedom Party and the conservative United National Party. The Judiciary is independent of the executive and the legislature. The politics of Sri Lanka reflect the historical and political differences between the three main ethnic groups, the Sinhala majority and the Tamil and Muslim minorities, who are concentrated in the north and east of the island.