In 1913, after the Balkan Wars, Skopje became part of Kingdom of Serbia, and after the First World War the city became part of the newly formed Kingdom of Serbs, Croats and Slovenes (Kingdom of Yugoslavia). In the Second World War the city was conquered by the Bulgarian Army, which was collaborating with the Nazi Germans. In 1944 it became the capital city of Democratic Macedonia (later Socialist Republic of Macedonia), which was a federal state, part of Democratic Federal Yugoslavia (later Socialist Federal Republic of Yugoslavia). The city developed rapidly after World War II, but this trend was interrupted in 1963 when it was hit by a disastrous earthquake. In 1991 it became the capital centre of independent Macedonia.