My research aims to explain the divergent outcomes of EU democracy promotion in Eastern Europe. It inquires: Why have EU democracy promotion efforts led to divergent outcomes in Eastern European countries? Given that the EU's motivation for promoting democracy is linked to the nexus between peace and democracy, this project traces the EU's impact on democracy and peace in Eastern Europe. It employs a historical institutionalism approach to identify critical junctures, mechanisms, and processes, explaining why the EU is successful in some countries, and limited in others.