According to About.com, Germany was not a major cause of the start of World War I. In fact, it was Austria-Hungary that first declared war on Serbia, leading to the beginning of WWI. Not all countries entered into WWI at the same time. Japan, Italy and the United States are examples of countries that took part in the war but were not involved from the beginning.
The assassination of Archduke Franz Ferdinand is generally considered the immediate cause that sparked WWI. This is because this assassination brought other items into play that historians list as the main cause of the war, such as alliances, nationalism, militarism and imperialism.
Ferdinand and his wife were assassinated in June of 1914 by a Serbian nationalist. This assassination was in protest of Austria-Hungary having control of Sarajevo, Bosnia. With Serbia demanding control over Bosnia and the assassination of Ferdinand, the Austria-Hungary government had little choice but to declare war on Serbia.
Due to the alliance that Russia had with Serbia, Russia started to mobilize as soon as Austria-Hungary declared war on Serbia. This caused Germany, which had an alliance with Austria-Hungary, to mobilize and declare war on Russia. Later, France was dragged into the war after Germany attacked the country through Belgium. This pulled Britain into the war, which was allied with both Belgium and France.