Napoleon, the Emperor of the French, destroyed the Holy Roman Empire in 1806, thereby establishing the basis for the ascent of the German Empire that was going to humiliate France in 1871.
Prussia and Austria fought hard to establish their leadership over Germany. The result was a militarized Prussian class that killed Germany once in the First World War, and then again with its support for Hitler.
“Of course” Adolf, from Austria of all places, dedicated his life to the nationalist cause, with the result that Germany was annihilate and Prussia airbrushed from history at the end of World War II.
Those are not the only ironies of history. The end result of the Christian Crusades was the undermining of the Byzantine Empire, and the opening up of Eastern Europe to the Ottoman Muslims. Nobody has killed as many Communists as Stalin, or as many Chinese as Chairman Mao, and since Tamerlane perhaps nobody has killed as many Muslims as Osama bin Laden and his loose “organization”.
I am sure there are many more examples of unbelievably unintended consequences. Hadn’t it been for the continuous slaughter, History would be a topic to laugh very hard about.