. The 1919 Versailles Peace Conference created new states in East Central Europe (ECE), but the imperfect implementation of the ‘one nation, one state’ formula resulted in more than twenty‐five million ‘unassimilable’ minorities. With the introduction of majoritarian democracy, this gave rise to what we term ‘ethnic reversals’: ‘formally dominant majorities’ suffered status decline, while previously ‘minoritised majorities’ found new political powers. Accordingly, the 1919 Minorities Treaties sought to manage these ‘ethnic reversals’ by instituting a liberal minority rights regime that tried to create both ‘tolerant majorities’ and ‘loyal minorities’. While the Treaties reflected the influences of Anglo‐American and Anglo‐American Jewish elites – the most notable voices of liberalism in an age of ethnic homogenisation – we suggest that in contexts of historical diversity with little institutionalised liberalism, ‘ethnic reversals’ raise issues that cannot be resolved within liberal conceptions of minority rights that rely solely or primarily on cultural protections.