Why Britain entered the First World War

Britain's entry into the First World War had no single cause. Belgian neutrality mattered because Belgian territory had long been central to British security. Alliance expectations, balance-of-power calculations, and repeated diplomatic misreading also narrowed every government's choices. Leaders and publics understood that a war between peer powers would be horrific, while the familiar claim that they confidently expected it to end by Christmas comes from later in the conflict. Each power had constrained itself through plans and promises, then overestimated its ability to control the consequences.