The breakup of the Ottoman Empire after the First World War came after a century of decline which saw it lose vast amounts of territory. But even in 1914, they were still in control of many strategically and symbollically important territories. They had the Strait of Marmara, and therefore the power to block Russia's Navy and Maritime Commerce, much to the chagrin of Russia and to the delight of everyone else.
Well, to be precise, there is a
Sea of Marmara and there are "the Straits", Bosphorus and Dardanelles connecting it to the Black and Aegean Sea.
"power to block Russia's Navy and Maritime Commerce" is a tricky issue because between 1856 and 1889 it was pretty much non-existent: even if Russia rejected Paris Treaty after the Franco-Prussian War construction of the Black Sea fleet was delayed, not to offend the Brits, until 1881 with the first barbette battleships being available in 1889 and the 1st turret-based by the early XX. While, of course, this did not prevent the British fear of the non-existing Russian Black Sea fleet sailing though the Straits with an ambitious purpose of dominating the Eastern Med (obvious confusion with the late XVIII), the
real issue was Russian fear of the Ottomans letting the 3rd party navies to sail into the Black Sea and attack Russian ports. The pre-wwi Russian naval buildup program on the Black Sea had been triggered by the Ottoman purchase of few modern battleships which would make the Black Sea fleet pretty much useless.
As for the maritime commerce, yes, this was an important consideration but keep in mind that most of that commerce had been conducted by the foreign ships and that the Ottomans were not obstructing it in a time of peace.
They had the Holy Land, with all cultural importance that carried.
But by the late XIX this was not a consideration for starting a war.
And they had the Persian Gulf, which we would find out had lots and lots of oil.
Presumably we are still in "pre 1900" forum and presumably you are talking about 1870's so this is non-issuer: oil exploration in the Persian Gulf started in 1929 with the 1st well starting functioning in 1931.
So what's the best way we could have something approaching the Treaty of Sevres where Turkey is reduced to a rump state by, say, 1870 with Russian control of Constantinople and British control of the Persian gulf? And what impact does this have on the world?
Actually, this is quite simple:
(a)
In the early 1850's Nicholas I does not behave as a jerk toward Napoleon III and Russia and France have a meaningful discussion regarding "the Sick Man in Europe".
(b) Palmerston is either pushed out of the British politics or recognizes that with an agreement between France and Russia Britain may miss its piece of a pie. Britain joins the alliance at which point you can come with any partition schema you wish. Of course, at the sight of an opportunity of getting something with no risk and effort, Austria joins the pact. Not sure what Britain is going to do with the Persian Gulf in the 1850's but probably there was still something of value to steal in the area. France & Russia are delineating spheres of interest in Levant (most of which goes to France with the agreement regarding a shared ownership of the Holy Places), Austria is getting pieces of the Balkans. Not sure how exactly Russia ends up with holding Constantinople unless its is permanently annexing all the coastal territory from the Danube to at least Bosporus but, to make it meaningful, to Dardanelles. On the Caucasus it can definitely get all or almost all Turkish Armenia. The Brits are getting Cyprus, Crete and whatever else they want and the loose pieces like Egypt, Arabia, etc. are falling apart just because the Ottomans can't hold them.
Consequences? Basically, with a little bit less of a paranoia among its political leadership Britain could get pretty much everything it got after WWI
with a minimal fighting. There would be additional fringe benefits for the future Entente like not having the Ottoman Empire as a significant military factor in the WWI (if it happens).