Why do some countries democratize while others do not? The issue of successful and failed democratization processes has long intrigued scholars of political science. Previous research has generated numerous theories about the factors necessary for a successful transition to democracy. This dissertation focuses on the democratic development of the post-Soviet region. When analyzing the past three decades of post-Soviet democratic development, the general pattern is increasingly autocratic. This dissertation examines the association between non-democratic regional organizations (NDROs) and democratic development, aiming to provide new insights into research on democratization, autocratization, and regionalism. Drawing on theories of authoritarian regionalism, the main research problem focuses on if memberships in Russian-dominated NDROs has played a role in the varying democratic developments in the post-Soviet region between 1991 and 2021. Using three different comparative analyses, this dissertation has uncovered findings that show that the impact of several factors in combination with each other has been essential in constructing the puzzle of democratization and autocratization in the post-Soviet region. The dynamics of the post-Soviet states’ relations with Russia, their geographical locations, the strength of their presidential systems, their memberships in NDROs, and their interactions with other regional actors have been important components in the democratic development of the post-Soviet region. For some states, at certain points in time, membership in NDROs has had an impact on the varying democratic development in the region, as either present or absent in conjunction with other variables. The dissertation argues that general, or region-based, assumptions on factors enabling regime transitions are difficult to make. Each state has a unique starting point shaped by its historical legacy, domestic circumstances, as well as regional dynamics.