The Imperium lost some land. In the east, it was not very much land except for Suzdal but it was barely acquired when the invasion began, so there was no real attachment to it. In the west, the land that was lost was joined into the new German Republic, which seemed to be hostile to the Polish Imperium. The Crimean Peninsula had been cut off from the rest of the Imperium by what was called by the Crimean Poles as the "Rossiyan Corridor" (OOC: a play on the post-WW1 "Polish Corridor

) and the port city of Odessa was also given to Rossiya. Many Poles fled these areas fearing repression, even though the Polish administrators, before leaving, had attempted to put their fears to rest. Noone really resented the Rossiyan Corridor - people resented the new Germany because it insulted Poland after it was recognized as sovereign by the Emperor.
Now, Norway was still in Finland. Poland could not and would not allow Finland, its only close and trustworthy ally - other than Yalta, of course - to be swalled up by the greedy nation that had hated Poland so much for such a long time. And the Finns were vastly outnumbered - 600 (Finland) vs. 5500 (Norway)? Finland did not stand a chance. Therefore, Poland would send in troops to push the Norwegians back into their own country and restore Finland.
Meanwhile, there was now a war going on between 2 non-European (cuz Greenland isnt really Europe, so...) superpowers for the position of major superpower on the continent of Europe, and it seemed that even the nations that really struggled and worked hard to maintain neutrality in this were being sucked into the conflict. Everyone was taking sides. Everyone except Poland (and maybe a little handful of other nations, but I dont kno what their names are, so...). Poland would not join Phoenicia because Phoenicia did not like Poland no more, but it would not join FNA either because they organized this whole multi-invasion of the Imperium and virtually crippled the nation, not to mention the fact that the Norwegians went across the border back to their own land for a quick breath and then came rushing back into Finland again - that way, they followed the Treaty of London by withdrawing first, and then blamed the Finns for supporting the Swedes in their uprisings and came back into Finland. They based their accusation on the fact that ONE of the Separatist soldiers happens to be a Finn. This does not mean that Finland supported the rebellion. The captive may have just been an ethnic Finn that lived in Norwegian areas already, or a mercenary that just happened to be Finnish. There are a lot of mercenaries and as we all know, mercenaries are not always loyal and not always loyal to their governments! This was unacceptable. Norway obviously thought that now, since Poland was significantly weakened, Finland would be left without Polish assistance because the Imperium would be worrying about itself rather than its allies. The Norwegians could not be more mistaken, because while Poland is indeed weakened, it will still not stand by and watch as one of its few allies is slaughtered.
Diplo
From Emperor Casimir IX of the Polish Imperium
To Finland:
Don't worry, friend. We are sending help against Norway! Their accusations are not justified at all and are just an excuse to keep invading you.
To Norway:
Withdraw your troops from Finland or we will withdraw them for you. You are obviously basing your allegation on a chance occurence that there was a Finn in the ranks of the Separatist troops. It could have simply been an ethnic Finn that had lived in Norway for years and decided to join the rebellion, or it could've been a Finnish mercenary! Mercenaries are not loyal. Just because he was Finnish does not mean that he was sent by the Finnish government! The Swedish Separatist sentiment may have been building up for years and you failed to address issues in Sweden that may and probably have created this rebellious sentiment. You are clearly fishing for excuses to keep invading Finland and getting more land!
To FNA:
We suggest that you tell Norway to retreat from Finland immediately! They are basing their allegation on a chance occurence that there was a Finn in the ranks of the Separatist troops. It could have simply been an ethnic Finn that had lived in Norway for years and decided to join the rebellion, or it could've been a Finnish mercenary! Mercenaries are not loyal. Just because he was Finnish does not mean that he was sent by the Finnish government! They are just searching for excuses for invading, occupying, and annexing Finland.
Orders
Give the FNA the 1 Economy level (the FINAL payment from the Treaty of London)
Increase economy by continuing to rebuild roads.
Send 3,500 troops into Finland to help the Finns and push the Norwegians back to the pre-war border.
Keep the rest of the troops guarding Polish borders.
Keep the Neo-Imperial Guard in Polish Crimea to maintain order and defend it in case of any attack by anyone.