In 1939, the Soviet Union unsuccessfully attempted an invasion of Finland, subsequent to which the parties entered into an interim peace treaty granting the Soviet Union the eastern region of Karelia (10% of Finnish territory), and the Karelo-Finnish Soviet Socialist Republic was established by merging the ceded territories with the KASSR. After a June 1940 Soviet Ultimatum demanding Bessarabia, Bukovina, and the Hertza region from Romania, the Soviets entered these areas, Romania caved to Soviet demands and the Soviets occupied the territories.