Supposing for whatever reasonable reason that the Ottomans stay neutral in World War I, what if any affect would this have on the course of events in Europe, Russia, and the middle east (and elsewhere if it has even bigger effects)
First, Turkey was a major drain on the Allies in WW I.
By closing the Straits, Turkey cut off Russian grain exports and screwed their economy, and also blocked shipments of arms to Russia.
Russia also had to fight a major campaign in the Caucasus.
Britain was sucked into three major campaigns: Gallipoli, Mesopotamia, and Palestine, with enormous costs.
It's not clear what Turkish neutrality means for Bulgaria; Bulgaria remained neutral till the Gallipoli campaign failed, then joined the CPs and knifed Serbia. This led to the Salonika campaign, which was another huge running sore for the Allies. Bulgaria might do that anyway, and it will be harder to bullyrag Greece into "joining" the Allies when the Allies aren't fighting Turkey.
But Bulgaria may stay neutral; Russia will be stronger, and the threat of Russia and Romania coming down would be a deterrent, with no offsetting support from Turkey (or from Germany as based in Turkey).
If Bulgaria remains neutral - Serbia holds out longer against Austria.
Romania may be induced to join the Allies sooner, and will not be attacked from the south. Romania can also import arms from the Allies.
Possibly Austria begins to fall apart in 1916. When Emperor Karl succeeded Franz Josef OTL in 11/16, he soon began seeking a separate peace. ITTL, that's even more determined.
At the same time, Russia should be stronger and not fall apart in 1917; or perhaps not till late 1917.
It does not seem likely that Germany will refrain from submarine warfare and provoking U.S. entry on the Allied side. That could precipitate Austrian withdrawal from the war, if Karl is scared enough. Germany might try to force Austria to keep fighting, as with Hungary in WW II, but I think that would backfire.
Germany can't fight on without Austria. So the war probably ends in mid-to-late 1917, just in time to avoid the Russian Revolution.
The settlement will be very different from OTL, of course. Romania would get what it did OTL (why not?) but not Moldova. Russia... would want Galicia, but probably has been driven out of Poland. Does Germany give it back?
Karl will try to hold Austria-Hungary together, but Hungary will break away, and probably the Czech lands. Italy will get Trentino and Istria; maybe not Sudtirol.
The situation in the Balkans is weird. OT1H Austria-Hungary is negotiating a peace, not falling to bits as OTL; OTOH, Serbia will be in a stronger position.
France will insist on Alsace Lorraine, of course. The Kaiser may be able to cling to power. Russia... Victory will not be sweet, and the returning troops may be radicalized.
For the Middle East - enormous differences, if only because vast numbers of people don't get killed. Turkey had the highest proportion of war deaths to total population of any major belligerent. Probably no Armenian massacres and almost certainly no Greco-Turkish War. Nonetheless, the Sultanate is on shaky footing. But I can't see how things go with such a radically different beginning. (Note also that Turkey doesn't regain the Caucasus territory lost in 1878.)
Arab nationalism hasn't even started, and probably doesn't start for another generation or so. The Saudis don't get control of the Holy Cities.
No Balfour Declaration. The Zionists however have made a start in Palestine.
If there is no Russian Revolution, then large scale Jewish emigration from Russia continues, which could be boost to Zionist settlement - if Turkey allows it.
Some broader economic effects: all of the major belligerents spend a good deal less on the war. Russia remains part of the conventional world economy. Britain may still be reduced to a debtor nation, but not as deep. Dunno about France. Germany probably gets off paying reparations. The U.S. is substantially less convulsed by the "total war effort".
Wilson (if he gets re-elected) will have much less influence on the peace settlement.