@alexmilman have a good point, further expansion didn’t really benefit Russia. But as Russia never did try to stop expanding, it raise the question where would Russia try to expand, if it did control Constantinople and who would it bring Russia into conflict with and could Russia expand places where it was a real benefit, instead of just a way to come into conflict with its neighbors.
Good questions and I wish I had good answers.
OK, up to the early XIX Russia was expanding:
1. Swedish Baltic provinces - opening ports for a direct access of the foreign traders to Russia plus the areas were generally more developed than Russia and did provide the useful cadres.
2. Poland - Belorussia and Ukraine had been more or less pushed down Catherine’s 5hroat by Austria and Prussia, Poland proper was economically attractive (and to a great degree this part of annexation was forced by ill-timed Polish patriotism).
3. Finland - need to protect St-Petersburg (and to improve PR after Tilsit fiasco)
4. Black Sea coast - need to stop the Crimean raids and to make available the good agricultural lands. You may notice that even the future wars were not considering a direct annexation of the European Ottoman Empire beyond Moldavia (more or less a “natural border”)
5. Caucasus - Russia got stuck with getting Georgia and a need to have secure communications with it so everything in between had to be conquered from Ottomans or Persia but conquests at the Persian expense stopped in Azerbaijan with the following trade agreements and “soft influence” (the Brits had been competing for 8nfluence there by the 1830s or maybe earlier). Persia was a trade partner well before Romanovs came to power.
6. Central Asia - markets for the Russian goods and stopping raids on the Russian territories
7. Far East - trade with China
During the wars of CII Russia was quite comfortable with an idea of the Austrians getting Principalities, which excludes grand schemes of getting Constantinople, etc. (Austria would be in between). War of AI against the Ottomans had been started by the Ottomans encited by Nappy and his main goal was to force the Turks to sue for peace so that he would have free hands against Nappy: the peace treaty was signed in 1812 and prior to that, even with the dramatic growth of the size of the Russian army, this theater got only limited number of troops because bulk of the forces was on the Western border. Which means that for the whole scenario to have a realistic chance
all policy of AI had to be drastically changed with the impact on the rest of Europe being so serious that any speculations about British, French and Austrian attitudes are pointless: there are multiple possible scenarios which would be shaping short and long term situation in Europe.
Now, in the best case scenario (Russia conquers Western coast of the Black Sea, gets land connection to the Straits and does not face an immediate opposition) what would be Russian gain outside of a mantra “the bigger, the better” (actually, even PI expressed an opinion that Russia is already too big to be efficiently governed and does not need further expansion)? Not sure if there is anything serious enough to justify the trouble.
On a positive side, Russia gets a direct access to the Med. Sounds great but “access” means “access for the navy” because Russia does not have a merchant fleet worth noticing and is not going to have it for a foreseen future. So, while the British navy is sailing here and there providing security for opening the new markets, the Russian navy is simply sailing here and there to no obvious purpose: who on the Eastern Med needs Russian grain, timber, iron, hemp, etc.? Its textile industry is on the early stages of growing and woolens are imported from Britain (there is some domestic production but it is not competitive even within Russia) and manufactured goods are of a poor quality and do not cover even the domestic market. Slave trade coming through Istanbul would be over.
Eventually, with Odessa growing into a major port (post 1819), Constantinople may become a transit port but Odessa would be a terminal and all the way to the end of the XIX the merchant ships would be predominantly British and French but not Russian so what is the point?
What else? Short of a genocidal scenario, Russia is getting city with more than a half of its population being hostile and, unlike Warsaw, not too skilled in producing anything useful from the Russian perspective. However, there is a need to fed them, which means that a portion of the Russian grain is not bringing in the British gold. Then goes a beauty: restoration of St. Sophia as an Orthodox Church with the obvious need to deal with a resulting revolt and future outbreaks of a religious fanaticism. Plus, there is a need to spend considerable money for the massive fortifications on both European and Asiatic side and permanently keep considerable number of troops there.
Potential gain from possession of the land bridge to Constantinople is one more question mark: the area is not wealthy (and Russia never even tried to conquer it) and ethnically diverse, which is going to produce more administrative problems. Creation of the rump states of Bulgaria and Walachia would mean eventual border issues which are going to appear in the worst moment possible.