 The Moscow Peace Treaty was signed on 12 March 1940 and went into effect the following day . Finland ceded a portion of Karelia — the entire Karelian Isthmus as well as a large swath of land north of Lake Ladoga . The area included Finland 's second largest city of Viipuri , much of Finland 's industrialised territory , and significant parts still held by Finland 's army — all in all , 11 % of the territory and 30 % of the economic assets of pre @-@ war Finland . Twelve percent of Finland 's population , some 422 @,@ 000 Karelians , were evacuated and lost their homes . 
