Ukraine and Belarus are two post-Soviet states and neighboring countries that, to some extent, demonstrate successful and failed democratization respectively. The purpose of the study is to, based on a theory-consuming approach, investigate which deep structural and proximate actor-oriented explanatory causes may constitute prerequisites and/or obstacles for democratization in these countries. The empirical material draws inspiration from Lachapelle and Hellmeier (2022), from which the explanatory factors are borrowed. The factors are categorized in this study based on relevant theories that Møller and Skaaning (2013) have outlined. Of the deep causes, Belarus' high degree of modernization speaks for the country's good conditions for democratization. Despite Belarus' superiority in the modernization factors, Ukraine has advantages in other deep causes, above all the very strong civil society. In Belarus, there is a lack of proximate causes that can favor democratization, while Ukraine has very favorable conditions – albeit with a high degree of corruption. The study confirms the hypothesis that deep and proximate causes co-vary with each other and with the outcome, but also contradicts, to some extent, an absolute relationship between modernization factors and other deep structural causes as well as the causal direction between proximate and deep causes and suggests an opposite causal relationship. Deep structural causes in combination and interaction with proximate causes determine the development of democracy in these countries. No single theory alone can provide answers to our questions.