In another thread, we were discussing the potential ability of the British Empire to have re-conquered the United States during the American Civil War (but let's not discuss that here). In that discussion, other wars of a similar time period were mentioned, like the Crimean War, the Sepoy Rebellion, some colonial wars in Africa.

It appears that, during the Pax Britannica between the Napoleonic Wars (which saw the mobilisation of tens of millions of troops, and 6.5 million casualties), and the First World War (which also saw the mobilisation of scores of millions of troops and tens of millions of deaths), the largest war fought anywhere in the world was the American Civil War.

Is that right? Any war between 1815 and 1914 is fair game. I've considered the Boxer Rebellion, the Russo-Japanese War (1 million v. 500k), the Second Boer War, the Franco-Prussian War (900k v. 1.2 million), etc. etc.

The American Civil War was, all told, ~2 million on the Union side vs. 1 million on the Confederate side. 750,000 deaths, not even including civilians. Is this the biggest war of the Pax Britannica?