The First World War was a failure of diplomacy.
In the years before the war the Great Powers of Europe competed intensely in politics and in military matters. Fear and distrust led to the outbreak of war.
The war changed the political shape of Europe fundamentally. Across the continent, monarchies disappeared: the Romanovs in Russia, the Hohenzollerns in Germany and the Hapsburgs of Austro-Hungary. After President Woodrow Wilson of the USA declared that all people had the right to self-determination, new states such as Yugoslavia and Poland established their independence.
In Britain a coalition brought the Labour Party into government for the first time. David Lloyd George became Prime Minister and was one of Britain’s most successful wartime leaders. By the end of the war, however, the once-dominant Liberal Party split and soon lost its place to the Labour Party as the main opposition to the Conservatives.
After the war, extreme political movements of the left and of the right arose across Europe. The struggle between them would influence European politics for decades to come.
The war, and especially the Treaty of Versailles that ended it, brought down the old order that had ruled Europe for generations and changed the balance of politics fundamentally.