A blast from the past, balance of power politics in Europe:
“The defense ministers of Sweden and Finland announced Thursday a new military cooperation agreement that could see the two countries go to war together in the event of an attack. The new relationship comes amid ongoing aggressive behavior from Russia in the region. Neither country is a member of the North Atlantic Treaty Organization (NATO) alliance, whose charter stipulates that an attack on one member is an attack on all, mandating a reaction from every allied nation.”
http://www.ibtimes.com/scared-russia-sweden-finland-make-war-pact-1821906
IR Theory & Practice 