Many historians believe that the buildup of armies in Europe at the beginning of the 1900s eventually led to the outbreak of World War I. What is their reasoning for this belief? The expansion of military power held by the world's navies led to shots being fired as navies entered enemy territory. The growth of armies led to to economic shortages as countries spent too much on warfare, causing revolutions. World War I began because the generals leading the armies of Europe were bored with peace and restless for combat. The race to build stronger weapons made countries anxious to attack before their enemies became too powerful