Stuart Bremer often reminded us that third parties - directly or indirectly - affect the initiation, evolution, and termination of conflict. He encouraged scholars to research the phenomenon of joining behavior further and personally investigated it. Questions about joining behavior are indeed deeply intertwined with a variety of theories of conflict. However, existing records on third-party interventions are limited to states' military involvement in conflict. The limitations imposed by the data can lead researchers to biased or incomplete conclusions about many international phenomena. We heed Bremer's encouragement and present here the results of an effort to collect new evidence on nonneutral (partisan) interventions in militarized interstate disputes for the 1946-2001 period. The data we present differ from existing records in that: (1) they provide information on both third parties' military and nonmilitary activities; (2) they broaden the notion of what constitutes a third party by including coalitions of states, intergovernmental organizations (IGOs), and nongovernmental organizations (NGOs); (3) they expand the investigation framework by recording interventions that occur before and after a militarized dispute. We test the usefulness of the data by exploring the issue of major powers' interventions in conflicts, as Yamamoto and Bremer did in their 1980 "Wider Wars and Restless Nights" article. We offer strong support for Yamamoto and Bremer's finding that major powers drag one another into ongoing conflicts and show how the data may help us raise and answer new and more complex hypotheses about third parties and the dynamics of joining behavior. Copyright © Peace Science Society (International).