Separation of powers should be the correct answer
The Abbasid Dynasty founded Baghdad around the year 762. The decision to relocate the Islamic capital from Damascus (the capital of the prior Umayyads Dynasty) came after the Abbasid rulers usurped regional power from their predecessors and thus sought to relocate power to a distant area. Baghdad would eventually become a flourishing city during the Abbasid period until the infamous Sacking of Baghdad by the Mongols in 1258.
Germans were using submarines and U-boats to bomb Allied trade vessels.
