Your website is a real beacon.
As I know , warfare according to Quran in three ways is permissible and transgression is forbidden but something always bother me :
Why muslims Conquered Persia , Byzantyine empire and even Spain ?! It was not a clear aggression ?!
Did Persian or Roman poor people ask help from muslims to free them from tyrant empires that they come ?! No!
Not Persia nor Byzantine empire did not need to conquer Hijaz and muslum capital , so why muslims in prophet companion-rashidin khalifehs era attacked and kill innocent people in theses countries ? (No war happen without killing)