Who is principally responsible for the current weakness of the Muslim Ummah: Is it the ruling systems and rulers, or the Muslims themselves?

The primary reason for the weakness of the Islamic Ummah lies in the state of the Muslims themselves. The calamities that befall them and their rulers are a consequence of their actions, as Allah Almighty says: "And whatever calamity strikes you, it is because of what your hands have earned." And as you are, so shall your rulers be. The fate of affairs rests with kings and their deputies, not solely due to their own shortcomings, but due to deficiencies in both the ruler and the ruled. Allah is Wise; He causes some wrongdoers to rule over others because of what they used to earn. The righteousness or deviation of souls is the root cause of the stability or crookedness of affairs. Indeed, Allah does not change the condition of a people until they change what is in themselves. If the servants fear their Lord and rectify their condition through faith and righteous deeds, He will grant them inheritance of the earth and make them vicegerents therein.