The emergence of the idea of Baltic Sea unity and of Baltic cooperation seem to be the issues which unify the two big epoch-making periods, the end of the First World War and the end of the Cold War. In both periods, the Baltic Sea connection has been seen to offer a coordinate for remapping the location of the eastern Baltic nations, the Estonians and Latvians, in particular. Why has the Baltic Sea area played so important a role as a construct of the new Europe? This is the question examined in this study, which focuses on the period after the First World War when the disintegration of European multinational empires meant a shift in the international system from the hegemony of a few great powers to the heterogeneity of small states. As a part of this process, the concepts of sovereignty and national self-determination were redefined by the small states themselves so that they would manage to find their place in the world of the great powers. One expression of this transition period was a lively Baltic cooperation, which attained an exceptional pitch of intensity in the Europe of its time.