For everyone who says that it's stupid to go to war while your country is starving, it's not.
Imagine your country has more people than it can feed. The solution is to secure more food or have fewer people. And the people who aren't getting enough food aren't the nobles or wealthy, but the poor. Starvation historically lead to rioting much of the time - off the top of my head it was a major cause of the French and Russian revolutions. So you have limited food and a bunch of angry starving peasants whom you're afraid might revolt. What do you do?
You find an enemy. You say, "this country is selfishly hoarding all the food that we need." You conscript the peasant men and tell them that they are fighting to secure food for themselves, for their families, for their country(though admittedly that concept didn't exist in the same way back then), and then you wage a bloody war. You have fewer peasants for sure, and likely more food, so that's your most pressing problem solved.
The foreign (muslim-coded) kingdom approached first, so we know that they find war disadvantageous enough that they would consider an alternative. Land or resource negotiation is definitely the best outcome here. Historically, the caliphate was known for its vast trading networks, its judges, its recordkeeping, and its mathematics. Resource wise, it had gold, salt(EXTREMELY important for food preservation), sugar, and textiles. So it'll be interesting to see what happens here.