Finland started cooperation for its own defensive reasons, not because both peoples speak Finnic languages. Defence plans involving Finland launching a massive assault against Leningrad if the Soviet Union started a war against both countries. However, the plan would also have required the participation of Latvia, and according to the Finnish military leader, Carl Gustaf Emil Mannerheim, the countries would have needed outside help from the League of Nations. Finland could not send troops directly to the Baltic countries, but a joint assault would have been possible through the Karelian Isthmus and/or from Poland.