War is an inevitable and important aspect of the game .... naturally! So it's important that you have some developed strategies for preparing yourself before attack, and defending yourself against being attacked.
An important aspect of this is ensuring you are well researched in combat skills through your academy. Completing these will provide you with critical boosts in scouting, training speed, troop attack and defense, and at the higher levels of research, troop health. The combat skills through your academy is also where you unlock higher tiers of troops when your Stronghold is levelled up to an appropriate level to do so.
