21 October

Western Front

 * The Yser: Critical day: Dixmude heavily bombarded and assaulted.
 * Arras also heavily bombarded and attacked.
 * The Argonne: French recovery begins.

Eastern Front

 * Poland: Germans begin retreat from Warsaw: Battle of Kasimiryev: Russki annihilates the Germans who had crossed the Vistula.

Political

 * Russia: State sale of alcohol abolished.
 * Great Britain: Reply to manifesto of German professors published.