The war erupted in 602 following a violent military coup in the Byzantine Empire. The army mutinied against Emperor Maurice and elevated Phocas to the throne, leading to Maurice's execution. Khosrow II, the Sasanian King of Kings who had regained his throne with Maurice's help a decade earlier, used the assassination of his 'friend and father' as a casus belli. Declaring his intent to avenge Maurice, Khosrow launched a massive invasion, capitalizing on the internal chaos in Byzantium to capture Syria, Egypt, and many fortified cities.
The Byzantine Emperor Heraclius reorganized the army, cut costs, and led daring counterattacks from Anatolia into Persian-held lands. Battles and raids turned the tide, and the Persians were pushed back after years of fighting.
By 628, both empires agreed to peace and returned captured territories. The war ended, but the long fighting drained soldiers, money, and supplies, leaving both sides weak just before new conflicts began in the region.