What annoys me is that there is not one authority with knowledge of treaties who can tell if there is a way to cancel the Montreux treaty.
What happens here on forum is guess work. Guessing is not good enough, we need facts.
We don't know what will happen de jure if Turkey cancel the Montreux convention. But we do know that there is not much that other countries can do if Turkey, with its current might that is ever increasing, annuls the convention.
Turkey has been suffering under Russian shenanigans for decades. Before Turkey joined NATO, the soviets were pressuring Turkey heavily about the straits and thus it pushed it into the NATO sphere. And even then, Russian aircraft carriers could freely pass the straits because they could als carry missiles and thus could be classified as 'aircraft carrying cruisers' while NATO carriers could not enter the Black Sea. Even after the collapse of the Soviet-union, the Russians kept threatening Turkey with their naval power in 1996 and subsequently in 2014 with the invasion of the Crimea. All the while Turkey was and still isn't capable of countering Russia in the Black Sea on an equal deterrence basis.
And for the cherry on top, the Turks helplessly watch as Russian war- and supply ships pass through the straits, arming the Syrian butcher and bombing Syrians that eventually flee to Turkey by the millions. Turkey is, like we say in dutch: 'mopping the floor with the tap running'.
How can Turkey counter Russian military power in the Black sea and the Mediterranean? Simple, annul the Montreux agreement and establish full sovereignty over the straits. Only with Turkish permission, warships of any nation can enter or leave the Black Sea.
A Russian military support operation for Syria would then become virtually impossible to sustain for the Russians, and would thus fail. But this is only possible if Turkey has sufficient conventional deterrence capability against Russia in the Black Sea (think groundlaunched LACM and AShM, longer range ballistic missiles, long range SAM, supersonic AShM) or it it allows NATO carriers and subs in the Black sea on a more permanent basis to pressure the Russians. But it is better for Turkey to build up its own capabilities against Russia, because it is already working on independent military capability.
Because of Turkeys' current might, the only country that could meaningfully protest against an annulling of the Montreux agreement in the Black Sea, is Russia. The other countries are aligned with Turkey and too weak to protest such a decision. And secretly the US and NATO would love it to be able to pressure the Russians in the Black Sea. It makes the Russians think twice before they start shit against Turkey or its surroundings.
And together with Istanbul canal, Turkey can also earn a lot of money with transit fees, investments, prime real estate and jobs. A double win for Turkey.
Russia has gotten away with a lot of shit against Turkey. It is time for Turkey to dish out some too.
