27 events the sources record for this year, grouped by region.
What happened
China (3)
Tibet invaded Songzhou; Hou Junji was made Grand General of the Dangmi Route to campaign against them, and the next month Niu Jinda defeated them at Songzhou. (New Book of Tang (Xin Tangshu), Annals 新唐書 卷002 太宗 貞觀12年8月)
In August 638, the Tubo crush the Dangxiang and Bailan qiang tribes; with some 200,000 men they camp on Songzhou's western border, and, claiming they came to fetch the princess, send an envoy presenting gold and silk. (Zizhi Tongjian (Comprehensive Mirror) 권195 638년 항)
In 638, the Tubo attack the city for more than ten days; Niu Jinda, as vanguard, strikes in September (Xinhai day) while the defenses are unready, routs the Tubo beneath the walls of Songzhou, and beheads more than a thousand. (Zizhi Tongjian (Comprehensive Mirror) 권195 638년 항)
Along the south bank of the Ganges, about three hundred li east, he reached the country of Champa; circumference about 4,000 li. (Xuanzang, Great Tang Records on the Western Regions Si-yu-ki (Beal 1884) vol.2 Bk X Champa)
Crossing the Ganges, about six hundred li east, he reached the kingdom of Pundravarddhana; circumference about 4,000 li. (Xuanzang, Great Tang Records on the Western Regions Si-yu-ki (Beal 1884) vol.2 Bk X Pundravardhana)
Crossing a great river, about nine hundred li east, he reached the country of Kamarupa; circumference about 10,000 li. (Xuanzang, Great Tang Records on the Western Regions Si-yu-ki (Beal 1884) vol.2 Bk X Kamarupa)
Twelve hundred to thirteen hundred li south, he reached the country of Samatata; circumference about 3,000 li, bordering the great sea. (Xuanzang, Great Tang Records on the Western Regions Si-yu-ki (Beal 1884) vol.2 Bk X Samatata)
About nine hundred li west of Samatata he reached the country of Tamralipti; circumference 1,400 to 1,500 li. (Xuanzang, Great Tang Records on the Western Regions Si-yu-ki (Beal 1884) vol.2 Bk X Tamralipti)
About seven hundred li northwest he reached the country of Karnasuvarna; circumference 1,400 to 1,500 li. (Xuanzang, Great Tang Records on the Western Regions Si-yu-ki (Beal 1884) vol.2 Bk X Karnasuvarna)
About seven hundred li southwest he reached the country of U-cha (Udra); circumference about 7,000 li, capital about 20 li. (Xuanzang, Great Tang Records on the Western Regions Si-yu-ki (Beal 1884) vol.2 Bk X Udra)
About 1,200 li southwest, passing a great forest, he reached the kingdom of Konyodha; circumference about 1,000 li, capital 20 li. (Xuanzang, Great Tang Records on the Western Regions Si-yu-ki (Beal 1884) vol.2 Bk X Konyodha)
Leaving al-Mada'in to found Kufa — from reed houses to brick houses (Al-Tabari, History of the Prophets and Kings Series I tom.5 sect.1 (Arg.) [india.history.resource.86986], Annus 17)