Complex sentence: Religion, ideology, and culture may also play in the favor of the enemy; non-combatants may prefer to side with them on basis of nationalism, ethnic connections, or simply a general dislike or even outright hatred of a foreign invading force.
Split into simpler sentences: Religion, ideology, and culture may also play in the enemy's favor. Non-combatants may prefer to side with them because of nationalism, ethnic connections, or general dislike, even hatred, of a foreign invading force.