Which country does Persia refer to? What does it have to do with the Tang Dynasty?

Persia, now Iran, is a big western country, which was called rest in peace in the Western Han Dynasty. In the seventh year of Zhenguan (633), Dashi (Arabia) invaded Persia, Persia was defeated, and King Ise fled. In the twenty-first year of Zhenguan, Yisi sent envoys to the DPRK for help. Because of the long distance, Emperor Taizong was not allowed to send troops. Ise was waiting for death, and Pirooz III fled to Toholo and sent a special envoy to help. Because of the distance, Tang Gaozong is still not allowed to send troops. Food soldiers retreat, Dong Bang escorted Pirooz III home. In the first year of Longshuo (66 1), he claimed to have been harassed by big food repeatedly and asked Tang to rescue him. Tang Gaozong established Persian Governor and appointed Pirooz III as Governor, which was regarded as a sign of rescue. In fact, the land of Persia has been occupied by grain, and the governor is just an empty name. During the reign of Xianheng (670 ~ 674), Pirooz III entered the DPRK and died in Chang 'an. The rest of Persia had a good impression on the Tang Dynasty. Xuanzong came to the Tang Dynasty for more than ten times, all paying tribute in the name of Persia, and all the way to Tang Daizong. Many Persians (mainly businessmen) lived and did business in the Tang Dynasty.