The outbreak of World War I in 1914 was precipitated by the rise of nationalism in Southeastern Europe as the Great Powers took up sides. The Allies defeated the Central Powers in 1918. During the Paris Peace Conference the Big Four imposed their terms in a series of treaties, especially the Treaty of Versailles.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): When did a stalemate occur in World War I?
unanswerable