To split an army into a smaller 1 - 49 army, you can garrison a castle with an army bigger than what the castle can handle. So like if you have a castle that can only handle 200 troops, if your army has more than 200 and you try to garrison the castle, it'll ask you if you want to split the army. Say yes and then you can send the 1 troop into that castle. From there you can have that 1 troop leave the castle and you now have a literal army of one to go destroy enemy crops. 😂