World War I was actually a largely European war. What made the war so important were the huge casualties caused no only by the duration, but the introduction of new weapns, including poison gas and rapid advances in the lethality of weapons. A whole generation of European men was largely killed in the fighting. The consequences were enormous. Empires and ruling families fell. Long held social systems collapsed. The Bollshevivks seized power in Russia. New countries based on nationality were created in Eastern Europe out of the old empires. The national hatreds that were spawned errupted in an even more destructive war 20 years later
Europe at the turn of the 20th centuy was prosperous and the center of the world intelectually and scientifically, chalenged industrially only by the United States. Most Europeans thouht that a general war was impossible. There was considerabl reason to think that this was the case.
The last major war, the Napoleonic War, ended in 1815. Wars had been subseuently fought in Europe during the 19th century, but they had been brief engagements between individual countries. Turn of the century Europe was inter-conected to an incrdible degree. Railroads had made possible economic interactions possible to a greater extent than ever before. The economic interconnections and the costs of war were such that many felt that a major war would never occur. Even the royal families of Europe, in part thanks to Queen Victoria, were cnnected, making war even more unlikely.
France as a result of German seizure of Alscae and Loraine in the Franco-Prussian War (1870-71) was Germany's mortal enemy, but without allies did not dare to challenge the Germans again. Germany and Austria-Hungary became known as the Central Powers. Germany's major ally was Austria in part because they were both German speaking nations.