Major British war between 1866 and 1875

What sort of conditions, starting no earlier than 1866, could lead to a major war for the British Empire between 1866 and 1875? Preferable opponents are France, Germany, or the United States, or a combination of any of them - however, any opponent is good enough, OTHER THAN:

- Russia,
- the Ottoman Empire
- any Balkan states,
- Austria-Hungary,
- or any states in present-day Italy.

Essentially, the point is that when the Russo-Turkish War happens (in 1875 in this timeline, starting with the Herzegovinian rebellion), the British should have much bigger concerns, and they won't be able to intervene on behalf of the Ottomans.
 
What sort of conditions, starting no earlier than 1866, could lead to a major war for the British Empire between 1866 and 1875? Preferable opponents are France, Germany, or the United States, or a combination of any of them - however, any opponent is good enough, OTHER THAN:

- Russia,
- the Ottoman Empire
- any Balkan states,
- Austria-Hungary,
- or any states in present-day Italy.

Essentially, the point is that when the Russo-Turkish War happens (in 1875 in this timeline, starting with the Herzegovinian rebellion), the British should have much bigger concerns, and they won't be able to intervene on behalf of the Ottomans.

Potential enemies:

1 - USA: tension mounting over US actions in the Civil War and fears of US military strength in GB; US does something stupid in Canada. Relatively unlikely, since the USA is occupied with Reconstruction.

2 - I'd like to say France, given the Franco-Prussian War, but Bismark probably won't let it happen if the British are in the mood to interfere on the continent. Maybe instead they go to war against Frace, too, because of some colonial skirmish.

3 - China: the 2nd Opium War lasts longer OR 2nd Indian Mutiny, perhaps sparked by a longer Opium War. Neither of these is likely in and of itself to keep the British from fighting a European war, but combined and if the former conflict has lasted quite some time then...who knows, it could happen.
 
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