Arguably, the most consequential war was the Crimean War of 1853–1856. The immediate effects of the war did not actually change the course of history— hundreds of thousands of people died, Russia lost the Danube Delta, Kars, Southern Bessarabia. However, the crucial, history-changing effects would only show up later.

Austria and Russia had been pretty good allies up until the beginning of the Crimean War— Russia had helped Austria quell the Hungarian Revolution of 1848, and expected Austria to return the favor sooner or later. But when Austria chose to stay neutral instead of supporting the Russian Empire, relations sort of broke down between the two. Because of this, Austria would go on to be politically isolated for the rest of the 19th Century and up until the beginning of the Great War.

See, the fact that Austria had no allies in the Austro-Prussian War meant that Bismarck’s Prussia was able to quickly gain the advantage and force Austria to sue for peace, giving Prussia a free hand with the German states. Had Austria joined the Crimean War on Russia’s side, even if the course of the war was not been altered, Russia would likely have remained friendly with Austria and may have stepped in to fight Prussia in the Austro-Prussian War. The German states being unified by Prussia without Austria’s consent would, therefore, have been much more difficult, if not altogether impossible.

In such a scenario, it is unlikely the Franco-Prussian War would have unfolded, either. No Franco-Prussian War means no ceding of Alsace-Lorraine to the German Empire (which would not have been formed, either) and no bombardment of Paris. No ceding of Alsace-Lorraine and no bombardment of Paris means no French desires for a war of revenge— a war in which France would punish Germany for “stealing” Alsace-Lorraine and humiliating France. Moreover, a Franco-Russian alliance would also have been unlikely, as France would not have to fear a German Empire, and Austria would still have been friendly with Russia.

And that’s just one side of the Crimean War’s effects, yet it could have been enough to prevent the First World War. Would you not agree? If Austria was on good terms with Russia in 1914, who would have been there to declare war on Austria if it decided to invade Serbia? And if the German Empire was never formed, who would have invaded France through Belgium, and why would the UK have joined the war? Would France have opposed Austria if Russia didn’t? World War I might still have happened, but it would have been extremely different.

The alliances would have been totally different. We might have Austria and Russia invading Serbia with the Italians attacking Austria from the southwest and the German states remaining neutral. Perhaps Prussia would have joined the war on Austria’s side and invaded some of the other German states. Would France have joined the war on the side of some of the German states? What about the UK? And it is unlikely that the USA would be involved in such a war. Things would have gone very, very differently. Perhaps World War I would not have taken place at all! And theoretically, there would be no World War II without a First World War.

And it was thanks to Sardinia Piedmont’s intervention in the Crimean War against Russia that France did not intervene in the Italian Unification. Had Sardinia remained neutral, things may have gone differently. Would Italy still have been united? Possibly. Perhaps we’ll never know, but all in all, the Crimean War had massive and long-lasting effects.