In 2019, US-China relations that had been characterized by a pattern of ups and downs over the past quarter century took a clear and possibly irreversible turn for the worse. This change has provoked debate about whether China and the US have already become rivals, perhaps adversaries, in a new cold war. I examine five underlying influences shaping the newly intensifying rivalry. These influences reflect key features of the international context within which the US and China find themselves (systemic or structural constraints) and the fact that the two rivals happen to be the US and China (national or unit-level attributes). Chief among the international constraints are the structural conditions of anarchy and the distribution of power that defines the system's polarity. The national attributes most relevant to understanding the evolution of US-China relations are the geography of the theater where the two countries' vital interests intersect and two aspects of their militarily relevant technological capabilities. Examining these five influences draws attention to reasons for some important similarities but also differences between the current rivalry and the Soviet-American rivalry of the Cold War. It makes clear that a Cold War II, if that is what is emerging, will not simply replicate the rivalry of Cold War I. Unfortunately, this examination also directs attention to some troubling new concerns about the distinctiveness of the new rivalry and the challenges they may present in the coming decades.