The German war plan called for a massive offensive against France that would pass through Belgium, but one of the big unknowns in German war planning was whether the Belgians would resist, and if so, how fiercely.

French strategists emphasized the importance of offense and planned to respond to a German invasion with an offensive of their own. British strategy increasingly revolved around joining with France in a ground war.

A look at how Germany and Russia planned to fight the Great War.

A survey of the most important reasons why the Great War happened and why the international order failed to prevent it.

Germany mobilizes and declares war on Russia and France. As German troops move into Luxembourg and Belgium, the British Cabinet comes around and joins the war.

Russia finds the Austrian ultimatum unacceptable. Austria, egged on by Germany, pursues war with Serbia anyway.

In the four weeks following the assassination of Archduke Ferdinand, the Austrian government slowly pondered its response. Meanwhile, in the rest of Europe, the murders were already being forgotten.

In the final days of peace, many European leaders were preoccupied with domestic problems as others debated whether war was inevitable, or obsolete.

Despite warnings of possible violence, the Austrian Crown Prince travels to Bosnia to observe military maneuvers. During a visit to Sarajevo, he and his wife are assassinated.

In 1914, with victory against the Turks secured, Serb nationalist extremists look north toward Austria.