Global goals to protect biodiversity, and national initiatives to form new conservation areas, are often followed by complex and conflictive processes when implemented on the regional level. A better understanding of disputed policy changes – both in terms of drivers and obstacles – is urgently needed to support the realization of international agreements and national environmental objectives. The aim of this paper is to identify and tentatively explain transformative moments and divergent outcomes in three marine national park planning processes in Sweden using a comparative approach. The study builds on theoretical assumptions about policy change developed within the Advocacy coalition framework (ACF). What combination of factors – triggering events, policy learning and negotiated agreements through brokerage - explains divergent outcomes in three different national park planning processes? The findings show that all factors matter for the turnout; however, in different combinations. Beyond triggering events, both policy learning and brokerage play an important role, with the former is especially important in complex conflicts and the latter in stalemate situations. The study contributes to knowledge on policy change and provides empirical insights critical to implement international and national conservation policy.