In 1870, the French were unaware of the distinction between mobilization (Mobilmachung) and concentration of forces (Strategischer Aufmarsch). They carried out both operations simultaneously, calling the former the “conversion from a peacetime footing to a wartime footing” and the latter the “formation of the army.”

On July 11, 1870, when he decided to take personal command and organize a single army out of the twenty-six divisions of eight different corps, Napoleon III was convinced that he could have 400,000 men at the ready within a fortnight. His optimism belied the fact that his secretary of war, Field Marshal Edmond Leboeuf, had informed him that it would be difficult to form an army of 250,000 men within two weeks time, that it was overly optimistic to expect 350,000, and that it was virtually impossible to hope for any more.

At this particular time, the Imperial Army consisted of 350,000 noncommissioned officers (NCOs) and enlisted men, including soldiers on leave but not counting the gendarmes. Part of the French armed forces was stationed outside of the country, particularly in Algeria (approximately 80,000 men) and Rome (8,000). It is true that, as early as July 8, the governor-general of Algeria received orders to prepare the troops of the African army for redeployment. The decision to recall the occupation corps in Rome was not made until August 2; actual troop movement did not take place until the beginning of September. In contrast, the regiments from Africa arrived fairly quickly and were able to take part in the battles in Alsace and Lorraine.