Bulgaria has a long and storied history. Hosting human habitation since the Bronze Age, it is believed that the first known tribes to settle in Bulgaria were the Thracians of Indo-European origin. The lands of Bulgaria were also ruled by the Roman and Byzantine Empires, respectively, and became part of the Ottoman Empire in the 1400s. Bulgaria gained its independence in 1908, sided with the Central Powers in the First World War, and with the Axis powers and then later with Russia in the Second World War. Following World War II, Bulgaria was part of the Eastern Bloc. In 1991, Bulgaria became a parliamentary republic and in 2007 joined the European Union.