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.