As far as I can find, the military casualties of the (decade-long) Napoleonic wars were around 3 million. The Crimean war caused close to 1 million casualties

As far as I can find, the military casualties of the (decade-long) Napoleonic wars were around 3 million. The Crimean war caused close to 1 million casualties in 3 years. https://en.m.wikipedia.org/wiki/Crimean_War https://en.m.wikipedia.org/wiki/Crimean_War The war involved Second French Empire, British Empire, Russian Empire and the Ottoman Empire. Perhaps there are other examples of major wars, but this one seems significant. EDIT: Outside of Europe, consider the Taiping Rebellion, with the highest deaths estimates at 30 million (or even higher!). The British and French got involved as well. https://en.m.wikipedia.org/wiki/Taiping_Rebellion https://en.m.wikipedia.org/wiki/Taiping_Rebellion