29 events the sources record for this year, grouped by region.
What happened
China (8)
Qi Prince Li You killed Quan Wanji and others and tried to establish independence from Qizhou, but he was captured by his subordinates. (Old Book of Tang (Jiu Tangshu), Annals 舊唐書 卷3 貞觀17年 3月)
Crown Prince Li Chengqian committed a crime and was demoted to commoner; Prince Jin Li Zhi (Gaozong) was installed as crown prince. (Old Book of Tang (Jiu Tangshu), Annals 舊唐書 卷3 貞觀17年 4月)
In the eleventh month of the second year, Soga no Iruka sends Kose no Tokota and others to attack Prince Yamashiro no Ōe at Ikaruga (Nihon Shoki (Chronicles of Japan) 日本書紀 卷第廿四 皇極紀 2年 단락101)
Prince Yamashiro no Ōe returns to Ikaruga-dera, and the commanders surround the temple with troops (Nihon Shoki (Chronicles of Japan) 日本書紀 卷第廿四 皇極紀 2年 단락104)
Passing rocky mountains and deserts to the north, some 500 li, he reached the country of Kie-sha (Kashgar); circumference about 5,000 li. (Xuanzang, Great Tang Records on the Western Regions Si-yu-ki (Beal 1884) vol.2 Bk XII Kashgar)
About 500 li southeast, crossing the Sita River and passing great stone cliffs, he reached the country of Cho-kiu-kia (Yarkand); circumference about 1,000 li, capital about 10 li. (Xuanzang, Great Tang Records on the Western Regions Si-yu-ki (Beal 1884) vol.2 Bk XII Yarkand)
Korean Peninsula (1)
The king tried to make peace with Goguryeo and take Silla's Danghang fortress to cut off the Tang route, but stopped when Silla asked the Tang for help. (Samguk Sagi (History of the Three Kingdoms) 卷28 義慈王 3年)
An introduction to the country of Tsaukuta: circumference about 7,000 li; its capital, Ghazna, has a circumference of about 30 li. (Xuanzang, Great Tang Records on the Western Regions Si-yu-ki (Beal 1884) vol.2 Bk XII Tsaukuta)
An introduction to the kingdom of Parsusthana: about 2,000 li from east to west and 1,000 li from north to south; its capital is U-pi-na (Hupian). (Xuanzang, Great Tang Records on the Western Regions Si-yu-ki (Beal 1884) vol.2 Bk XII Parsusthana)
After three more days' journey, descending a pass, he reached Andarab; the former land of Tokhara, with a circumference of about 3,000 li. (Xuanzang, Great Tang Records on the Western Regions Si-yu-ki (Beal 1884) vol.2 Bk XII Andarab)
Following valleys and mountain passes northwest for some four hundred li, he reached Khost, a former land of Tokhara. (Xuanzang, Great Tang Records on the Western Regions Si-yu-ki (Beal 1884) vol.2 Bk XII Khost)