Luna, this is a basic formula for attacking neutrals
3 -> 2 = 2
1 + 2 -> = 1
Basically, if you attack a 2 with a 3, then 2 armies are left, and if you attack with a 1 and a 2, 1 army is left. It is more beneficial to attack with 3s, instead of a 1 and a 2.