The middle tier of states and the Russia–Ukraine war.

This article examines the concept of the 'middle tier of states' proposed by Halford Mackinder in 1919, its failure to prevent German–Soviet Union rapprochement in the interwar years, its recent revival and its geopolitical implications. Mackinder's 'heartland thesis' comprises two interrelated parts: the geopolitical significance of the heartland, and the middle tier of states, which he suggested could counteract the pernicious impact of the heartland. Although the middle tier of states paralleled the 1919 Versailles settlement in east-central Europe, its failure to play the role that Mackinder suggested has never been properly investigated. Over the past decade, the middle tier of states has been revived by a range of regional cooperation projects in east-central Europe, while the Russia–Ukraine war attests to its necessity and viability in the current context. The Russia–Ukraine war has shown that a strengthened middle tier of NATO and European Union states will not just reshape the geopolitical landscape of Europe but will have significant implications for world politics. [ABSTRACT FROM AUTHOR]