It started with some polish citizens raiding town in minskan rus at the start of the TN release, and despite that nothing much happened. Later on Bialystok claimed part of the border with Grodno, relations became for that reason shaky. then Poland started an expansion eastwards, the expansion was deep into claimed minskan rus' territory. As a result cutting off Mukachevo from the rest of minskan rus. Unlike byzantium no agreement was reached and soon Poland started to lose interest in negotiations and ignored. A short time later NATO collapsed so some towns thought Minskan rus went to war with Poland but the declaration of war ironically happened later.
Poland led some troops into a town in Minskan rus, and Grodno did an awesome effort against the poles, massacring Polish troops. Despite minskan rus often being outnumbered by Poland the battles were still lost for Poland. One of the towns that was on the polish side was convinced to switch side. More raids on Poland continued, with success.
Battle of Tarnopol
Poland then gathered 5-10 troops and marched on the town planning to join Minskan rus. Only one person from MInskan rus was fighting atm. Outnumbered between 5-1 and 10-1 this town lost that battle.
Later on raids in Poland happened, the stability of Poland became shaky
The leader of Minskan rus proposed a peace offer that would make Poland unclaim the towns in Minskan rus claimed territory, some gold and not expand into Minskan rus territory. Poland didn't respond
The stabillity of poland fell apart and a new nation formed called "Polish state" was in war with Poland.