Yuwen Chengdu and the other generals led their armies to the western border of the Western Turks, eyeing the Sassanid Empire to the west.
Yazdegerd, ruler of the Sassanid Empire, was already overwhelmed by the Arab Empire's attacks. Years of military defeats had left his empire on the brink of collapse.
After learning the news, Yazdegerd spent an entire day thinking alone. In the end, he made an astonishing decision: his entire empire would surrender to Great Wei, though not unconditionally.
Yazdegerd proposed three conditions:
First, after the Sassanid Empire surrendered, Great Wei had to treat its subjects well, granting them the same treatment as its own people.
Second, the lives of Yazdegerd and the members of his royal family had to be spared.
Third, Great Wei had to send troops to destroy the Arab Empire.
After hearing the interpreter relay these conditions, Yuwen Chengdu said, "Wait until I report this to Great Wei's emperor of great virtue. He will decide."
Yuwen Chengdu then dispatched a messenger to Daxing City, riding at full speed on a mission of the utmost urgency.
A month later, Cheng Yaojin received the news and readily agreed to the Sassanid Empire's requests.
Another month passed before Yuwen Chengdu received Cheng Yaojin's decree and accepted the Sassanid Empire's formal surrender. His armies began moving into the empire, while twenty thousand elite soldiers escorted Yazdegerd and his royal family to Daxing City.
Yuwen Chengdu led eight hundred thousand troops to garrison the Sassanid Empire's cities.
Standing atop the walls of Baghdad, the Sassanid capital, Yuwen Chengdu listened to the interpreter's explanation and said, "So the western strongholds, including Damascus and Jerusalem, have all fallen to the Arab Empire?"
"That is correct, General," the interpreter replied awkwardly.
"So the Sassanid Empire has only half its territory left," Yuwen