The purpose of this article is to re-evaluate the military spending dynamics leading to the First World War, namely to explore the impact of the declining military and economic leadership of the UK and the economic emergence of the USA. Individual countries responded to threats from perceived enemies and spillovers from potential allies rationally, yet often going beyond the bounds of traditional alliances. In a sixteen-country system, the military reticence of the UK and USA encouraged higher military spending by other states, which suggests that Germany was not responsible for the arms race alone. Aggregate systemic military spending also incurred higher individual spending levels, whereas alliance impacts were not consistent.