Let's say the Swedes win a very decisive victory at the Neva in 1240. Alexander Nevsky dies (probably known ITTL simply as "Alexander"), the Novgorodian army is routed with very heavy losses.
Now, contemporary sources claim the Swedish aim was the conquest of Novgorod, but that is obviously not realistic. But they will now definitely control the mouth of the Neva and Ladoga, which probably severely weakens Novgorodian trade.
What happens next? I assume the Teutonic Order will still try to expand to the East, would such a weakened Novgorod be able to resist? If not, how far can the knights go? Coupled with the Mongol invasions, what would this mean for Russia as a whole and Russian Orthodoxy in particular? Could Novgorod be gradually conquered and Catholicized?
The main problem with a premise is that, AFAIK, there is no trace of that expedition on the Swedish side and it seems that on the Russian side its first mentioning is in the chronicle of the XIV century and is void of any meaningful details (how is it likely that the name of the Swedish leader was “Spiridon”?) and the “classic” description of the alleged battle belongs to the XVI century and seems to be a part of the PR campaign promoting Alexander as a founder of the Muscovite ruling dynasty. This source is seemingly the first one which uses nickname “Nevsky” (depending upon the source, this nickname either was given to different prince of this name or was referencing to the estates that Alexander and his family owned on the Neva River). So there are no
contemporary sources on either side related to this
alleged event.
Realistically, there were numerous small-scale border raids conducted by all regional entities so some skirmish could happen
As far as the trade was involved, Novgorodian international trade started in X-XI centuries and during that period the closest trade relations were with Norway. In the XII the main partner was Gotland and starting from the early XIII the Hanseatic cities. In other words, there was no interest on any side involved to cut or minimize the existing trade and, as later experience demonstrated, the Novgorodian merchants had been quite happy with a schema in which the foreign merchants had been coming to Novgorod to buy and sell their goods. Novgorodian part started with carrying the goods from the coast to Novgorod by the boats (and getting paid for the service) and ended with carrying the purchased goods from Novgorod to the coast. There would be a serious unhappiness on many sides if somebody would try to interfere into this schema because weakening the trade would mean lesser profits for the Swedish and German merchants.
Now, as far as the evil Teutonic Order is involved, strictly speaking it was on a wrong side of Lithuania and the stories of its expansion to the East are grossly exaggerated. The entity involved were the leftovers of Livonian Brothers of the Sword that had been incorporated into the Teutonic Order and better known as Livonian Order (white on the map). It did not have numbers needed for any serious conquest and most of its time and energy had been spent upon the quarrels with Archbishop of Riga (to whom it was formally subordinated) and other local entities. The most advertised engagement, so-called Battle on Ice, in a reality was an ordinary border encounter led by the Bishop of Dorpat, whterritory was raided by the Novgorodian troops under Alexander. Some members of the Livonian Order did participate in it but there were no plans beyond repelling the looters. Not that a size of the armies involved (and a number of the knights) would allow any serious conquest. What
was happening in a reality, was
political game with Pskov. It was an independent principality until 1230 after which it became subordinated to Novgorod and was
directly ruled from it until mid-XIII after which it started inviting its own princes again. Small wonder that in 1240 not everybody in Pskov was happy with the situation and that there was a party looking for the Livonian Order as an option. As a result, in the summer of 1240 Pskov accepted
two Order’s brothers as city administrators. Which resulted in a retaliatory action from Novgorod: in 1242 Pskov was returned under the Novgorodian control and territory of the Bishopric of Derpt was invaded and looted. The Bishop raised whatever troops he could, defeated one of the looting bands and then was defeated himself. The mysterious invading “Germans” of the official imperial/Soviet history who presumably threatened Novgorod itself (*) never were fully identified.
The Mongolian factor. The Novgorod Republic voluntarily submitted to the Mongols and paid tribute in 1241. From that point on invasion by the <whatever> Order and pretty much anybody else (with the possible exception of the ASBs and even this is not guaranteed) would mean the Mongolian involvement: attack on Khan’s vassal was an offense to the Khan. In the XIII century a number of the suicidal maniacs even among the military orders and clergy was too limited to launch a major war with the odds being that bad. Actually, at some later time there was an idea of attacking Novgorod which initially generated some enthusiasm but at the news that the GH is sending it’s troops to the area the “crusade” was speedily disbanded. 😂
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(*) Officially, it looked this way. The “Germans” (of unidentified origin and numbers) took castle of Koporie (see below) and advanced within 30 km from Novgorod. At which point Novgorod decided to call back Prince Alexander (who was expelled from Novgorod in previous year and was in Pereslavl-Zalessky, approximately 400 km away from Novgorod). Alexander sent to them his brother, Andrew, who was rejected and Alexander was asked for the second time after which he arrived with his troops. All that time the evil “invaders” did not move a step closer to Novgorod. Now, look at the size of Koporie and try to figure out how many troops it could hold. Now, if somebody still seriously believes in that scenario (actually, millions of people did thanks to the skillful propaganda), I have a very nice bridge for sale. 😂
