The French win the Franco-Prussian War and Wilhelm I is not able to unify the German states. The Protestant north and Catholic south become even more divided and a German Empire never exists. There cannot be a World War I because the Dual Alliance of 1876 is never formed between the Kaiser and the Austro-Hungarian Empire, the cause of most of the Entente alliances leading up to WWI.
I'm thinking of a war between France and an Anglo-Russian alliance over Africa. The French back the Boers causing the British to attack French colonies in West Africa. Somehow the Russians are thrown into the mix, delaying the Russian Revolution of 1905.