Editing Franco-Prussian War (section)

==French Army incursion==

===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}}

===Occupation of Saarbrücken===
{{main|Battle of Saarbrücken}}
[[File:Franco-Prussian-War Phase 1 toSedan.svg|thumb|upright=1.7|Course of the first phase of the war up to the [[Battle of Sedan]] on 1 September 1870]]
Napoleon III was under substantial domestic pressure to launch an offensive before the full might of Moltke's forces was mobilized and deployed. Reconnaissance by Frossard's forces had identified only the [[16th Division (German Empire)|Prussian 16th Infantry Division]] guarding the border town of [[Saarbrücken#19th century|Saarbrücken]], right before the entire Army of the Rhine. Accordingly, on 31 July the Army marched forward toward the [[Saar River]] to seize Saarbrücken.{{sfn|Wawro|2003|pp=85–86, 90}}

General Frossard's II Corps and Marshal Bazaine's III Corps crossed the German border on 2 August, and began to force the Prussian 40th Regiment of the [[16th Division (German Empire)|16th Infantry Division]] from the town of Saarbrücken with a series of direct attacks. The Chassepot rifle proved its worth against the [[Needle gun|Dreyse rifle]], with French riflemen regularly outdistancing their Prussian counterparts in the skirmishing around Saarbrücken. However the Prussians resisted strongly, and the French suffered 86 casualties to the Prussian 83 casualties. Saarbrücken also proved to be a major obstacle in terms of logistics. Only one railway there led to the German hinterland but could be easily defended by a single force, and the only river systems in the region ran along the border instead of inland.{{sfn|Wawro|2003|pp=87, 90}} While the French hailed the invasion as the first step towards the Rhineland and later Berlin, General [[Edmond Le Bœuf]] and Napoleon III were receiving alarming reports from foreign news sources of Prussian and Bavarian armies massing to the southeast in addition to the forces to the north and northeast.{{sfn|Wawro|2003|p=94}}

Moltke had indeed massed three armies in the area—the Prussian First Army with 50,000 men, commanded by [[Karl Friedrich von Steinmetz|General Karl von Steinmetz]] opposite [[Saarlouis]], the Prussian Second Army with 134,000 men commanded by [[Prince Friedrich Karl of Prussia (1828–1885)|Prince Friedrich Karl]] opposite the line [[Forbach]]-[[Battle of Spicheren|Spicheren]], and the Prussian Third Army with 120,000 men commanded by Crown Prince [[Friedrich III, German Emperor|Friedrich Wilhelm]], poised to cross the border at Wissembourg.{{sfn|Howard|1991|p=82}}