Main actors were the Entente, which included the Russian Empire, the French Republic and the United Kingdom; and the Central Powers, submitted by Germany, Austria-Hungary, the Ottoman Empire and Bulgaria. Germany wanted war exactly as much as France or Britain. Russia, Austria-Hungary and the Ottoman Empire were slightly less interested, provided that they were the weakest links in the conflict.
The proclamation of war took place against the background of the Franco-Prussian War, when France suffered a catastrophic defeat. This has become a national disgrace. In addition, France agreed to pay Germany an indemnity of 5 billion francs. To a large extent this money went to the development of the German economy, which subsequently by the 1890s led to its unprecedented growth. “It was the idea of revenge, which combined all the Third Republic, born in the crucible of the Franco-Prussian War.” (Sivers, Desnoyers, Stow, p. 524). The nation was united by the idea of return of Alsace and Lorraine.
Britain was concerned about the economic dominance of Germany in Europe and the world. By the 1890s Germany had the highest GDP in Europe, pushing Britain into second place. The British Government couldn’t accept this fact, given that for many centuries Britain was a "workshop of the world", the most economically developed country.
The reason for the war was the assassination of the Austrian Archduke Franz Ferdinand. June 28, 1914 in Sarajevo he was mortally wounded by a Serbian nationalist, member of the organization "Young Bosnia" Gavrilo Princip. The Austrian government accused Serbia of the murder and then the Serbian government was handed an ultimatum. It was not accepted by Serbia and became a pretext for declaring Austria-Hungary war on Serbia on 28 July 1914. Austria-Hungary was supported by Germany. Russian Empire stepped in to defend Serbia. August 1 1914 Germany declared war on Russia. France and Britain entered the war later.
The main fronts were West Front, where German troops were fighting against the British, French and Belgian troops, and the East Front, where Russian troops resisted the combined forces of the Austro-Hungarian and German armies. Human, raw materials and food resources of Entente significantly exceed the resources of the Triple Alliance (or as it is otherwise called, the central unit), so the chances of Germany and Austria-Hungary to win the war on two fronts were insignificant.
In Germany, a master plan was developed by Alexander von Schlieffen and was called "blitzkrieg". It implied prompt defeat of France, and then Russia. This plan failed due to the lack of resources. State of the German economy didn’t allow it to wage a long war on two fronts, and this is what she had to do throughout the war. “After the US entry into war on April 6 1917 Germany's position was completely hopeless and even Russia's withdrawal from the war could not change the situation” (Sivers, Desnoyers, Stow, p. 537). In addition, by signing the Brest peace, Germany was forced to keep under military control her new land - it also required human resources. So the answer to the fall of Triple Alliance in 1918 is that Germany failed to implement "blitzkrieg” plan and that Austria-Hungary failed to wage war against Russia effectively.
Peter von Sivers, Charles A. Desnoyers, George B. Stow. (2011). Patterns of World History, brief edition, Vol. 2, 522-541