It's normal for Royal in East Asia to take concubine from minor states for political reasons, for example, King Rama V of Thailand have 152 wives, many of them were for political reason either for local politics or international politics.
They use artillary in siege combat albeit a magic one so they should be somewhat familiar with concept of explosion.
Well they don’t even need knowledge about explosive they just need to know concept of traps and when to use them which was common since antiquity.
Drone is autonomous no need to learn and land mine is very easy to use they don't even need to bury it themselves just know when to press a button. The defensive systems were already in place since before they move in.