The area of today's Austria has been inhabited since at least the Paleolithic period. Around 400 BC, it was inhabited by the Celts and then annexed by the Romans in the late 1st century BC. Christianization in the region began in the 4th and 5th centuries, during the late Roman period, followed by the arrival of numerous Germanic tribes during the Migration Period. Austria, as a unified state, emerged from the remnants of the Eastern and Hungarian March at the end of the first millennium, first as a frontier march of the Holy Roman Empire, it then developed into a duchy in 1156, and was made an Archduchy in 1453. Being the heartland of the Habsburg monarchy since the late 13th century, Austria was a major imperial power in Central Europe for centuries and from the 16th century, Vienna was also serving as the Holy Roman Empire's administrative capital. Before the dissolution of the empire two years later, in 1804, Austria established its own empire, which became a great power and one of the largest states in Europe. The empire's defeat in wars and the loss of territories in the 1860s paved the way for the establishment of Austria-Hungary in 1867.
After the assassination of Archduke Franz Ferdinand in 1914, Emperor Franz Joseph declared war on Serbia, which ultimately escalated into World War I. The empire's defeat and subsequent collapse led to the proclamation of the Republic of German-Austria in 1918 and the First Austrian Republic in 1919. During the interwar period, anti-parliamentarian sentiments culminated in the formation of an Austrofascist dictatorship under Engelbert Dollfuss in 1934. A year before the outbreak of World War II, Austria was annexed into Nazi Germany by Adolf Hitler, and it became a sub-national division. After its liberation in 1945 and a decade of Allied occupation, the country regained its sovereignty and declared its perpetual neutrality in 1955.
Austria is a federal parliamentary republic and representative democracy with a popularly elected president as head of state and a chancellor as head of government and chief executive. Austria has the 13th highest nominal GDP per capita with high standards of living. The country has been a member of the United Nations since 1955 and of the European Union since 1995. It hosts the Organization for Security and Co-operation in Europe (OSCE) and the Organization of the Petroleum Exporting Countries (OPEC) and is a founding member of the Organisation for Economic Co-operation and Development (OECD) and Interpol. It also signed the Schengen Agreement in 1995, and adopted the euro currency in 1999. (Full article...)