From the Peloponnesian War, the Napoleonic Wars, to the Cold War, multilateral alliances have been one of the strongest instruments to shape the international order. But they do not always form in response to common threat. Why did NATO form in the face of Soviet threat, but the Pacific Pact – which was meant to be an Asian NATO – failed to develop even after the Chinese Communist Party won the Chinese Civil War in 1949? Why did the Triple Entente emerge as a counterweight to Wilhelmine Germany, but the same countries that comprised the alliance engaged in buck-passing as Nazi Germany expanded? In essence, why do certain balancing alliances form and not others? This dissertation seeks to clarify the nature of the collective action problem in multilateral balancing alliance formation. I argue that alliance formation against a large threat entails solving a specific collective action problem. Security from balancing becomes a threshold public good, and this creates disincentives for less powerful states to initiate an alliance or to join one. To overcome this problem, a group of states requires an “anchor” – a state whose power matches that of the adversary – to facilitate alliance formation. The anchor assures states that are on the fence that achieving security from balancing would be viable. Moreover, the anchor ameliorates free-riding by adding elements of "club goods" to the potential alliance. To demonstrate my argument, I examine three periods of alliance formation: early-Cold War Western Europe, early-Cold War Southeast Asia, and contemporary Southeast Asia in the context of the South China Sea conflict. In all these cases, there existed a growing regional threat with clear offensive intent (the Soviet Union and China); the threat was adjacent to medium and small states; and the participation in balancing by an extra-regional great power (the US) was possible. I show how different US actions changed the way regional states perceived the viability of balancing, and how specific American policies altered the incentives for intra- and extra-alliance free-riding. Together, they contributed to the formation of the North Atlantic Treaty Organization and the Southeast Asia Treaty Organization. Understanding the dynamics of multilateral balancing alliance formation has important policy implications. Throughout the past decades, Chinese power has been growing exponentially and China's foreign policy assertiveness increased in tandem. But it is unclear if a regional balancing alliance will coalesce, as many of China’s neighbors choose accommodation or hedging as their strategies. This dissertation, which applies especially to great power politics in the modern era, will elucidate factors that facilitate the emergence of a multilateral balancing alliance, as well as conditions that could hinder its inception.