Hungary became a Christian kingdom in A.D. 1000 and for many centuries served as a bulwark against Ottoman Turkish expansion in Europe. The kingdom eventually became part of the Austro-Hungarian Empire, which collapsed during World War I. The country fell under communist rule after World War II. In 1956, Moscow responded to a Hungarian revolt and announcement of its withdrawal from the Warsaw Pact with a massive military intervention. Under the leadership of Janos KADAR in 1968, Hungary began liberalizing its economy, introducing so-called "Goulash Communism." Hungary held its first multiparty elections in 1990 and initiated a free market economy. It joined NATO in 1999 and the EU five years later.