The years immediately after the collapse of the Soviet Union were characterized by high hopes for an expansion of the liberal world order and for lasting peace. In the meantime, discord between western democracies, led by the US, and non-democratic states has been increasing. In the present article, I ask in how far these tensions have reached the working level of international cooperation in the United Nations (UN). Specifically, I present the first large-N study of co-sponsorship that includes all UN resolutions drafted between 1994 and 2017. First, my results reveal that regime type became increasingly relevant for co-sponsorship of UN resolutions starting at the turn of the millennium. Second, I find that cooperation among non-democratic states increased during the first years of the millennium, but I find a restoration of democratic cooperation since 2006. Third, I find that these trends are especially relevant with regard to cooperation over national security.