When did the stalemate of World War 1 begin?

The stalemate of World War I began in late 1914, particularly after the First Battle of the Marne in September, when Allied forces halted the German advance towards Paris. This led to the establishment of trench warfare on the Western Front, where both sides dug in and faced each other in a prolonged and grueling conflict. The stalemate persisted for much of the war, resulting in heavy casualties and little territorial change.