Major events leading to WWI and major events of WWI

June 28 Assassination of Archduke Franz Ferdinand of Austria, heir to the Austro-Hungarian throne, who was killed in Sarajevo along with his wife Duchess Sophie by Bosnian Serb Gavrilo Princip.

August 2–26Germany besieges and captures fortified Longwy "the iron gate to Paris" near the Luxembourg border, opening France to mass German invasion

September 5–12First Battle of the Marne. The German advance on Paris is halted, marking the failure of the Schlieffen Plan.

December 24–25In some sectors of the Western Front, an unofficial Christmas truce is observed between German and British forces.