The offensive French military strategy in World War I known as Plan XVII was initially created by Ferdinand Foch. The offensive plan used brute force and a mystical belief in the French "élan" or "fighting spirit." General Joseph Joffre adopted this plan upon becoming commander-in-chief in 1911.

After the Franco-Prussian war of 1870, the French had lost the provinces of Alsace and Lorraine to the German empire. This created a spirit of revanchism in France, and one of the main aims of Plan XVII was to recapture Alsace and Lorraine. In order to do this, four French armies would advance on either side of Metz and Thionville. This left only one army to defend northern France, but French planners were convinced that Germany would not invade through Belgium, as this would lead to British involvement (in the Treaty of London, the United Kingdom had guaranteed Belgian neutrality).

Unfortunately for the French, the Germans regarded the Treaty of London as a mere "scrap of paper" (and thought the British would do so as well), and their Schlieffen plan called for an attack through Belgium and northern France in order to encircle Paris.

When the war broke out in 1914, the execution of Plan XVII ended in total failure. The German defense of Alsace-Lorraine turned out to be of much better quality than expected, and within a few weeks, the French were back in their starting positions, while the Germans had advanced almost unopposed through Belgium and northern France and were threatening Paris. Only the fact that the German high command diverted troops to the Eastern Front and to a counterattack in Alsace-Lorraine (which was in turn repulsed by the French), allowed the French and their British allies (who had adhered to the Treaty of London and thus declared war on Germany after the German invasion of Belgium) to halt the German advance in the First Battle of the Marne.

External Links

• First World War.com A map of the French and German war plans