1) Growing Nationalism: The late 19th and early 20th centuries saw a wave of nationalism sweep across Europe. This was due in part to the industrial revolution, which led to increased economic growth and a sense of national pride. At the same time, there was a rise in nationalist movements in the Balkans, which had been under Ottoman rule for centuries. These movements sought to create independent states for the various ethnic groups in the region.
2) Imperial Rivalry: The major European powers were also competing for control of colonies and resources in Africa, Asia, and the Middle East. This led to increased tensions between the powers, particularly between Britain and Germany. Germany felt that it was being left out of the colonial spoils and wanted to increase its power and prestige.
3) Militarism: The European powers had also been building up their military forces in the years leading up to the war. This was due to a combination of factors, including nationalism, the arms race, and the growing threat of war. The arms race was particularly intense between Britain and Germany, who were both building up their navies.
4) The System of Alliances: The European powers were also divided into two alliances: the Triple Alliance (Germany, Austria-Hungary, and Italy) and the Triple Entente (Britain, France, and Russia). These alliances were designed to provide mutual protection in the event of war. However, they also made it more difficult to resolve conflicts peacefully, as each alliance was backing its allies in their disputes with other countries.