Kavad II vs Leo I the Thracian

Kavad II, then known as Sheroe, led a coup against his father Khosrow II, imprisoning and later executing him. This act ended Khosrow's long reign and the Sasanian-Byzantine war, but plunged the empire into civil war and decline.

Kavad II ordered the execution of 17 of his brothers to eliminate potential rivals to the throne. This massacre decimated the Sasanian royal family and weakened the dynasty's legitimacy, contributing to the empire's instability.

Kavad II negotiated a peace treaty with the Byzantine Empire, ending the decades-long war. The treaty restored pre-war borders and returned the True Cross to Jerusalem, but the Sasanian Empire was left exhausted and weakened.

Leo I was crowned Eastern Roman Emperor by Patriarch Anatolius of Constantinople. This was the first time a Byzantine emperor was crowned by a patriarch, establishing a precedent for the role of the Church in imperial coronations and strengthening the bond between church and state.

Leo I, in cooperation with the Western Emperor Anthemius, launched a massive naval expedition against the Vandal Kingdom. The campaign ended in a catastrophic defeat at the Battle of Cape Bon, costing the empire immense resources and weakening its military position.

Leo I ordered the assassination of the powerful Alan magister militum Aspar and his son, who had dominated the Eastern court for decades. This act ended the Germanic influence over the Eastern Roman army and solidified Leo's authority, but also led to a brief civil war.