World War I was the result of leaders' aggression towards other countries which was supported by the rising nationalism of the European nations. Economic and imperial competition and fear of war prompted military alliances and an arms race, which further escalated the tension contributing to the outbreak of war.
Nationalism
Imperialism
Bismarck and Alliances
The Triple Entente, an informal coalition between Great Britain, France and Russia, now countered the Triple Alliance. International tension was greatly increased by the division of Europe into two armed camps.