Can anyone explain me how the heck the gamemechanics work in battle?

And I'm not even getting started on using the buffs for your own attack or diminishing enemy attack or health or whatever.

Just when sending scouts, how is it determined whether an attack is succesful or not? I've had enemies launch a spy-attack on me and succeed, even though I have WAY more spies in my city then they attacker has.

Same goes for attacks and defense on tiles or cities. It seems like the attacker pretty much always wins, unless he's outnumbered by more than 10-1 or so.

I can't make any kind of sense of how the outcome of a battle is decided and that's extremely annoying since it means its hard to make any kind of strategy that involves defense.