Why are the countries of Polyna and Rosya at war in the novel, Uprooted?

The two countries are at war because a prince from Rosya is believed to have lured Queen Hanna away from Polyna. It is more likely that both were corrupted by a book and that they acted on that corruption. The war has raged for decades and has depleted both countries, but neither is willing to let it go. When the people of Polyna are reminded of the treachery after Queen Hanna's rescue, they are immediately prepared to rush into war again.