In 1917, Communists took over the Russian Empire. Their leader became Lenin. In 1928, he wanted to expand that Communism to the Kingdom of Yugoslavia, Hungary, Austria and some other countries. A revolution was carried out in the Kingdom of Yugoslavia in 1929. In June 1929, a world economic crisis began. In hope of rescue, Bulgaria, Romania, Czech and Slovakia Kingdoms, Kazakhstan, Mongolia and ten other countries joined the USSR. In October the 25th 1930, Yugoslavia joined and the USSS was formed. Their leader was Lenin, who almost got killed by a cold in 1924.