Temporary capital of Lithuania during the invasion of Poland, to Lithuania according to the Soviet–Lithuanian Mutual Assistance Treaty. Since then Vilnius has been the capital of the Lithuanian SSR and then independent Lithuania. Lithuania refused to have diplomatic relations between Poland and Lithuania until the ultimatum of 1938. Railroad traffic, telegraph lines or even mail could not cross the Polish–Lithuanian border. Lithuania continued to declare Vilnius as its capital in all official documents, including the constitution. Since the city was controlled by Poland, all Lithuanian authorities were transferred to the city of Kaunas, which became the seat of the government. To reconcile reality with
National symbols of Lithuania Soviet occupation of Lithuania, the Lithuanian flag and the national anthem were replaced; the Lithuanian Coat of Arms was not shown in official capacities. On the other hand, in keeping with the Soviet policy of encouraging what were seen as harmless expressions of ethnic identity, Lithuanian national costumes were often featured on postal stamps and elsewhere. Lithuania was occupied by Soviet Union in 1940-1941, later it was controlled Nazi government during World War II and was a Soviet Socialist Republic from 1944 until 1990. The latter situation is generally seen by Lithuanians as an occupation. Public displays of both the