What are the consequences of new actors in the political arena? Recent research suggests that the emergence of radical right parties (RRPs) can defy long established democratic norms, with consequences for the behavior of both voters and political elites. We study whether that is part of a broader pattern by which new actors challenge the political establishment, provoke electoral backlash and increase polarization. With radical policy positions and new forms of organizing, Green parties were the first disruptors of post-war European party systems. However, little is known about the consequences of their emergence. We argue that Green party success threatens established norms of politics and thus provokes a backlash effect among conservative constituents. Whenever Green parties enter politics, conservatives are mobilized and subsequently turn out in higher numbers, which contributes to electoral polarization. We identify this effect with a difference-in-differences design on a newly compiled dataset based on voting records from Germany. While plenty of research emphasizes the role of the emergence of RRPs, our results suggest a more general pattern when new political actors emerge. Our findings become particularly relevant in a time of polarization and fragmentation across Western democracies.