Well seems like some of you didn't understand why the king want his heir to have vengeful spirit to the kingdom.
Here just think of it like this you doing gambling against this dude you know you can lose and you do lost but it didn't change the fact you would love to have it back as you know human greed and all that sort of stuff, there's also his integrity as a leader would be questioned by other countries ,because they let their territories taken just like that and they can't even let it go as it may set precedence to other countries to also try get their territories because they may think they are weak and wont fight back anyway
Here just think of it like this you doing gambling against this dude you know you can lose and you do lost but it didn't change the fact you would love to have it back as you know human greed and all that sort of stuff, there's also his integrity as a leader would be questioned by other countries ,because they let their territories taken just like that and they can't even let it go as it may set precedence to other countries to also try get their territories because they may think they are weak and wont fight back anyway