By the early 20th century, military spending had reached unprecedented levels, with Germany, France, Russia, and the United Kingdom leading the way. Each country was developing new strategies, weapons, and tactics in order to gain an advantage over its rivals. This competition also spurred technological advancements in submarines, aircraft, and long-range artillery, which would later prove decisive on the battlefields of World War I.
The intense rivalry and suspicion generated by the arms race contributed to the growing hostility and nationalism that pervaded Europe at the time. Each nation was fiercely protective of its interests and sought to defend its territory and power at any cost. The alliances and ententes that had been formed among the major European powers further solidified these divisions and created a web of obligations that made it difficult for any one country to back down from a confrontation without losing its allies.