How did the pre-1914 arms race increase tensions before World War I?

The pre-1914 arms race increased tensions because governments saw rivals' military expansion as a threat and responded with preparations of their own. Mistrust led to costly spending on larger forces and more powerful weapons. This made war more dangerous, but did not make the decision to fight unavoidable.

Follow how each step in the Anglo-German naval competition encouraged the next:

A German naval planning memorandum from February 1900 explains the logic of a 'risk fleet': even a stronger opponent should fear that attacking Germany would cause losses large enough to endanger its own position. The aim was to use naval strength to influence British choices. From Britain's perspective, however, the same fleet could look like a danger requiring more ships and closer cooperation with other powers.

This is often called a security dilemma: preparations described as protective by one government can make another feel less secure. That does not mean both governments had identical aims or equal responsibility.

Competition also involved armies. Germany expanded its army in 1913, while France adopted three-year military service. Leaders worried not only about present strength but about whether a rival would be stronger in future. Military plans and mobilisation schedules could then increase pressure for early decisions during a crisis. France's law of 7 August 1913 gives concrete evidence of the additional commitment demanded from its conscripts.

Keep the limits of this explanation clear. Governments could build weapons to deter an attack, and earlier crises had ended without a general war. Weapons did not issue ultimatums or declare war: political leaders did. In 1914 the assassination crisis, decisions in Vienna and Berlin, Russian mobilisation and other governments' responses turned tension into war. The arms race helps explain why that situation was dangerous; it cannot replace an explanation of those decisions.

Build your own explanation with the arms-race exercise in the First World War origins questions. Show how one country's preparations could increase another's fears, while keeping the decision to go to war separate from military competition.