<Tr> <Td_colspan="2"> Calling code </Td> <Td> + 7 012 </Td> </Tr> <Tr> <Td_colspan="2"> Today part of </Td> <Td> Lithuania </Td> </Tr> <P> The Lithuanian Soviet Socialist Republic (Lithuanian SSR; Lithuanian: Lietuvos Tarybų Socialistinė Respublika; Russian: Литовская Советская Социалистическая Республика, Litovskaya Sovetskaya Sotsialisticheskaya Respublika), also known as Soviet Lithuania or Lithuania was a republic of the Soviet Union . It existed from 1940 to 1990 . </P> <P> Established on 21 July 1940 as a puppet state, during World War II in the territory of the previously independent Republic of Lithuania after it had been occupied by the Soviet army on 16 June 1940, in conformity with the terms of the 23 August 1939 Molotov--Ribbentrop Pact . </P>

When did lithuania become part of the soviet union