In 1900, the capital had only 70,000 inhabitants (at the time Serbia numbered 2.5 million). Still, by 1905, the population had grown to more than 80,000 and, by the outbreak of World War I in 1914, it had surpassed the 100,000 citizens, disregarding Zemun, which still belonged to Austria-Hungary. The first-ever projection of motion pictures in the Balkans and Central Europe was held in Belgrade in June 1896 by André Carr, a representative of the Lumière brothers. He shot the first motion pictures of Belgrade in the next year; however, they have not been preserved. The first permanent cinema was opened in 1909 in Belgrade. The First World War began on 28 July 1914 when Austria-Hungary declared war on Serbia. Most of the subsequent Balkan offensives occurred near Belgrade. Austro-Hungarian monitors shelled Belgrade on 29 July 1914, and it was taken by the Austro-Hungarian Army under General Oskar Potiorek on 30 November. On 15 December, it was re-taken by Serbian troops under Marshal Radomir Putnik. After a prolonged battle which destroyed much of the city, starting on 6 October 1915, Belgrade fell to German and Austro-Hungarian troops commanded by Field Marshal August von Mackensen on 9 October of the same year. The city was liberated by Serbian and French troops on 1 November 1918, under the command of Marshal Louis Franchet d'Espèrey of France and Crown Prince Alexander of Serbia. Belgrade, decimated as a front-line city, lost the title of largest city in the Kingdom to Subotica for some time. After the war, Belgrade became the capital of the new Kingdom of Serbs, Croats and Slovenes, renamed the Kingdom of Yugoslavia in 1929. The Kingdom was split into banovinas and Belgrade, together with Zemun and Pančevo, formed a separate administrative unit. During this period, the city experienced fast growth and significant modernisation. Belgrade's population grew to 239,000 by 1931 (with the inclusion of Zemun), and to 320,000 by 1940. The population growth rate between 1921 and 1948 averaged 4.08% a year. In 1927, Belgrade's first airport opened, and in 1929, its first radio station began broadcasting. The Pančevo Bridge, which crosses the Danube, was opened in 1935, while King Alexander Bridge over the Sava was opened in 1934.