When the conflict broke out on 15 July 1870, France and Prussia had both acceded to the 1864 Geneva Convention. The ICRC established an International Agency for Aid to Wounded Millitary Personnel in Basle whose purpose was, in particular, to facilitate the channelling of assistance, in cash and in kind, which soon flooded into the city. To this end the Agency used staff who did not simply bring aid close to the battlefields; they also gathered information about the wounded and the most pressing needs. From 31 July, the Agency set up a service for the exchange of correspondence between prisoners of war and their families.

The ICRC also took steps to ensure the repatriation of seriously wounded prisoners, some 2,600 of whom were sent home through Switzerland.

The successive defeats of the French army led to the lengthy detention of several hundred thousand prisoners of war. The International Committee provided assistance, published lists of names and searched for soldiers who had disappeared.

During the conflict of 1870, the International Committee carried out tasks which have remained core activities ever since:

• sending delegates to conflict areas
• compiling lists of prisoners of war
• repatriating the wounded
• tracing missing persons
• delivering messages to those separated by war
• channelling relief to conflict victims