The Germans invaded France, but were stopped at the Battle of the Marne (September 1914). The British Expeditionary Force (BEF) helped to stop the Germans at the Battle of Mons (23 August 1914). The Russians invaded Germany but were destroyed at the Battle of Tannenberg (August 1914).
The War of Attrition (1916 ‒ 1918)
On the Western Front, both sides dug a 400-mile line of trenches from Switzerland to the English Channel. Soldiers had to put up with constantly being wet, being pestered by rats, and illnesses.
The Fighting Ends
There was a stalemate (neither side could defeat the other). On the Western Front, attacks on the German trenches led to huge casualties. Britain's attempt to open up a 'Second Front' at Gallipoli in Turkey was a failure.
Huge battles, eg Verdun and the Somme in 1916, Passchendaele in 1917, lasted many months. Thousands of men died or were wounded. New weapons, eg poison gas, tanks and aeroplanes failed to make much effect.