There is an option to declare war to other countries, but this option is not available in this version yet, maybe in the future update.
The problem is what if the player has impregnated Queen Apelia and Queen Varea? They could not attack Amagal and Begus. It would be nice to leave at least 1 neighboring country to become enemy.
About slave problem perhaps Brad's friend in the capital of Dorgania can help. I feel like there are still quests about slavery in the future update. That's just my opinion :)