How can international cooperation be maintained when faced with actors outside the regime? I analyze this question in the context of the Export Credit Agreement. This agreement aims to limit price competition among Export-Import Banks of OECD governments by establishing minimum price levels. Since 2010, member governments have complained about unfair competition by Chinese state-subsidized export credits. Consequently, members have tried to incorporate China into the agreement. Interestingly, China is not the first instance of outside competitors threatening to undermine cooperation: In the 1980s, Japan also offered subsidized export credits to stimulate their export industries. The US and European countries were able to incorporate Japan into the regime in the 1980s, but appear unable to do the same with China today. I analyze this difference in outcomes. I suggest that the interplay between domestic politics within the hegemon as well as the challenger determine the international dynamics of cooperation. Incorporation of an outsider is possible if divisions among the various ministries of the challenger government can be exploited to incentivize collaboration. Conversely, when member governments are internally divided, the challenger cannot be co-opted. Extensive archival evidence of internal government documents offers strong support for my theory.