This game nobody understands, but the troops of your garrison must be proportional. In lich what resists most is, 7 units of scorpions, 8 units of spiders and 3 units of acolytes to withstand 1 attack in the desert with the technology investigated. Skeletons appear before scorpions, are destroyed and resources are lost. Similarly, if a lich has more mummies, acolytes, than spiders and scorpions, appear before and are destroyed because they are not tanks. In my opinion, the best way to defend yourself is to know that troops are the ones that appear when they attack you and not have as a priority to investigate only one troop.