After the end of the First World War, in 1919, the Allies met and, as part of the Treaty of Versailles, forced Germany to accept the complete blame for starting the Great War. However, the question of whether or not Germany was to blame is a lot more complicated.
Before the question can be answered, it is important to look at the situation in Europe at the time before the First World War started. Europe was divided by two alliances: the Triple Alliance, of Germany, Austria-Hungary and Italy and the Triple Entente, consisting of Great Britain, France and Russia. The Triple Entente countries had been established for a long time and Britain and France had many overseas colonies and huge empires. They were quite happy with the situation in Europe and would not have much reason to start a war, although France was keen to regain the industrial Alsace-Lorraine area, lost to Germany in a recent war. However, this does not automatically mean that Germany was solely to blame. None of the countries in the Triple Alliance was completely happy with the status quo. Germany and Italy were newly formed and wanted their own empires and Austria-Hungary was divided, with inhabitants of many ethnic groups, and wanted to be more stable. The Alliance System was supposed to make sure that a war did not happen, because the risks involved would be too great. Instead, it made sure that, when two countries became involved in a dispute, the whole of Europe was drawn into a war.
Britain had been the major naval power in the world ever since the Battle of Trafalgar in 1805. It needed a powerful navy to control its many colonies, and did not become unnecessarily involved in costly wars, to concentrate on its empire. In 1898, the German Kaiser, Wilhelm II, increased the tension between Britain and Germany by announcing his intention to build a navy. Britain did not see why Germany needed such a large navy concentrated in the North Sea (Britain's ships were spread all over the world), despite the German navy being smaller than Britain's.