Editing Franco-Prussian War (section)

===Preparations for the offensive===
[[File:FrancoPrussianWarFrontierJuly1870.jpg|thumb|Map of the German and French armies near the common border on 31 July 1870]]
On 28 July 1870 Napoleon III left Paris for [[Metz]] and assumed command of the newly titled Army of the Rhine, some 202,448 strong and expected to grow as the French mobilization progressed.{{sfn|Howard|1991|p=78}} [[Marshal MacMahon]] took command of I Corps (4 infantry divisions) near [[Wissembourg]]; Marshal [[François Certain Canrobert|François Canrobert]] brought VI Corps (4 infantry divisions) to [[Châlons-en-Champagne|Châlons-sur-Marne]] in northern France as a reserve and to guard against a Prussian advance through [[Belgium]].{{sfn|Howard|1991|pp=69, 78–79}}

A pre-war plan laid down by the late Marshal Niel called for a strong French offensive from [[Thionville]] towards [[Trier]] and into the Prussian Rhineland. This plan was discarded in favour of a defensive plan by Generals [[Charles Auguste Frossard|Charles Frossard]] and [[Barthélémy Louis Joseph Lebrun|Bartélemy Lebrun]], which called for the Army of the Rhine to remain in a defensive posture near the German border and repel any Prussian offensive. As Austria, along with Bavaria, Württemberg, and Baden were expected to join in a revenge war against Prussia, I Corps would invade the [[Palatinate of the Rhine|Bavarian Palatinate]] and proceed to "free" the four South German states in concert with Austro-Hungarian forces. VI Corps would reinforce either army as needed.{{sfn|Wawro|2003|pp=66–67}}

Unfortunately for Frossard's plan, the Prussian army mobilised far more rapidly than expected. The Austro-Hungarians, still reeling after their defeat by Prussia in the Austro-Prussian War, were treading carefully before stating that they would only side with France if the south Germans viewed the French positively. This did not materialize as the four South German states had come to Prussia's aid and were mobilizing their armies against France.{{sfn|Howard|1991|pp=47–48, 60}}