• Finland: Russia attacked Finland on 30 November 1939, and the Winter War lasted until 13 March 1940.
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  • Poland: Russia attacked Poland on 17 September 1939, and occupied the eastern part of the country afterward.
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  • Lithuania: invaded by the Soviet army on 15 June 1940.
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  • Estonia: invaded by the Soviet army on 16 June 1940.
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  • Latvia: invaded by the Soviet army on 16 June 1940.
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  • Romania: "The Soviet occupation of (the regions of) Bessarabia and Northern Bukovina took place from 28 June to 3 July 1940, as a result of an ultimatum by the Soviet Union to Romania on 26 June 1940, that threatened the use of force." (quotation from the Wiki article about the Soviet occupation of Bessarabia and Northern Bukovina)