Paasikivi–Kekkonen line

The Paasikivi-Kekkonen doctrine refers to a foreign policy doctrine established by Finnish President Juho Kusti Paasikivi and continued by his successor Urho Kekkonen, aimed at Finland's survival as an independent sovereign, democratic, and capitalist country in the immediate proximity of the Soviet Union.

The principal architect of Finland's postwar foreign policy of neutrality was Juho Kusti Paasikivi, who was president from 1946 to 1956. Urho Kekkonen, president from 1956 until 1981, further developed this policy, stressing that Finland should be an active rather than a passive neutral.

Finland and the Soviet Union signed the Paris Peace Treaty in February 1947, which in addition to the concessions of the Moscow Peace Treaty provided for:

In April 1948, Finland signed an Agreement of Friendship, Cooperation, and Mutual Assistance with the Soviet Union. Under this mutual assistance pact, Finland was obligated, with the aid of the Soviet Union, if necessary, to resist armed attacks by "Germany or its allies" (i.e., NATO) against Finland or against the Soviet Union through Finland. At the same time, the agreement recognized Finland's desire to remain outside great-power conflicts. This agreement was renewed for 20 years in 1955, in 1970, and again in 1983. This allowed Finland to retain independence in internal affairs, e.g. a multiparty parliamentary system, and not to join the Eastern Bloc. However, joining NATO or other overt alliance with the West was out of question and foreign policy was often limited.

...
Wikipedia