France, certainly France. The French attempted to pester the British into recognizing the Confederacy with them, but failed to do so. (The French did not want to upset their ally (Britain), and decided against doing it alone). The French intervention in Mexico is going on during this time period, and actually affects American foreign policy (ex. Seward expresses disapproval with the action, but does not escalate it, due to the American Civil War). So seeing as the French intervention in Mexico was 1862-1867, one could argue that they should be added.
Mexico is in North America. ._.
The Austrians could be argued, but not very well. A Hapsburg reigned as Emperor of Mexico (Maximilian I (1864-1867)) because he was placed on that throne by the forces of Napoleon III (1853-1871) of France. Better to add France than Austria.