World War I began in 1914 after the famous assassination of Archduke Franz Ferdinand. But the Great War undoubtedly did not just happen. There was build up to the catastrophe that began way back to the times of Bismarck.
During the German Unification, Bismarck had used a war with France to include the South German States into his German Empire. But in the process, he took the region of Alsace-Lorraine from the French, as well as a gigantic indemnity of two billion francs. Bismarck had created hostile relations with the French. But he also tried to make sure that France could not get its revenge by keeping good relations with all the world powers (except for Great Britain which was uncaring of European affairs at that time). To keep Russia and Austria-Hungary out of the trouble, he made the Three Emperors League (an alliance) in 1873. However, there was a problem with this alliance; Austria-Hungary and Russia had long been rivals over dominance of the Slavs.
Germany ended up losing Russia as an ally, and in 1879, she formed the Dual Alliance with Austria-Hungary. Later in 1881, this alliance included Italy under the terms that if France were to invade one of them, the other two would help. This alliance was called the Triple Alliance. To make sure that Germany would not have to fight a war against France and Russia at the same time, Bismarck signed the Treaty of Reinsurance with Russia in 1887, ensuring neutrality in the case of a war with a third nation.
But the Dual Alliance was the only alliance which actually helped Germany in war. Even before he had made the alliance with Italy, she had made a defensive alliance with France that it would prevent it from aiding Germany in a war with...