Sir Edward Gray, British Foreign Secretary at the time, is said to have remarked, literally on the eve of the German invasion of Belgium in 1914, “The lamps are going out all over Europe. We shall not see them lit again in our time”.
He was right.
WWI is so interesting, as all of the elements of a maturing age came to a head. Old monarchies old regimes and modern weapons colliding on the European stage where so many battles had been fought before, only this time the old military tactics were no match for the progress made in weaponry such as machine guns and advanced artillery.
It took 4 years of slaughter before military thinking and technology advanced to a point where trench warfare could be breached.
the Russians could continue fighting the Turks in the Caucus and the Iranis, while the Austrians fought the Turks in the Balkans
With this state gone, the conflicts between Russia and the others increased -- and needless to remind you, this was encouraged by the UK and France who fought alongside the Moslem Turks against Russia in the Crimean war
Also, in the Balkan war, Bulgaria had a chance to conquer constantinople and the Brits intervened
Finally, note that on the eve of World War I, the English were supplying two destroyers to the Ottomans which would have enabled the ottomans to stand up to Christian Russia
The roots of World War I and II also lie in the French Revolution -- or rather in Napoleon's destruction of the Holy Roman Empire: before Napoleon there were 300 different states, duchies, princelets, bishoprics, free cities etc. in "Germany" with no central push.
The Austrians put some kind of "control" which was a very loose confederation. The Prussians were trying to muscle in with their militaristic life, but were kept at bay.
What Napoleon did was to end this disunited Germany -- he reduced the states to just 26 and he failed to dismember Prussia. He set the seeds for a united Germany united under the military of Prussia instead of a Germany that was more philosophical and commercial. Tsar Alexander (who was more German than Russian in blood if not in thinking) acquiesced in this by liberating large sections of Germania from France and by destroying many of the kingdoms (like Saxony) and giving them to Prussia
AT the same time the French revolution created the idea of a nation-state where everyone in a state was the same in language, culture etc. --> prior to the French revolution only about 10% of France spoke French (or rather Parisian French), the rest spoke O'il langauges or Basque or Gascon or Brittany or Alsation etc. There was forced Francification -- and this pushed the English to destroy Cornish and aim to destroy Welsh, Gaelic etc. and the Germans to replace all of the various Germanic dialects with Standard German (while aiming to destroy Polish) and the Russians to implement forced Russification.
The only large Empires that did not do this were Austria-Hungary, the Ottoman Empire -- they had too many different languages and cultures
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So these three strands dating from the late 1700s all tied in together: a lack of a buffer state between Muscowy and Germania, a united Germany under Prussia and nationalism. World War I was inevitable