7 events the sources record for this year, grouped by region.
What happened
China (4)
Wu Zetian was given the honorific title Divine Sage Emperor, and Emperor Ruizong was lowered to Huangsi (the Zhou was founded). (Old Book of Tang (Jiu Tangshu), Annals 舊唐書 卷6 天授1年 9月)
The state name was changed to Zhou and she ascended the throne as Holy Divine Emperor; Ruizong was demoted to Heir Successor. (New Book of Tang (Xin Tangshu), Annals 新唐書 卷004 則天·中宗 天授1年9月)
In August 690 (Xinwei day), twelve members of the imperial clan are killed, including Li Ying, Prince of Nan'an, and the two sons of the former crown prince Li Xian are whipped to death; the Tang imperial clan is nearly extinguished, and the young ones are exiled to Lingnan. (Zizhi Tongjian (Comprehensive Mirror) 권204 690년 항)
In 690 (Yiyou day), the honorific title 'Shengshen Huangdi' is presented; the emperor (Ruizong) is made heir and given the Wu surname, and the crown prince is treated as a grandson. (Zizhi Tongjian (Comprehensive Mirror) 권204 690년 항)
Japan (1)
In the tenth month of Jitō 4 (690), an edict praised Ōtomobe no Hakuma of Chikugo for having been captured by Tang troops during the Baekje rescue campaign. (Nihon Shoki (Chronicles of Japan) 日本書紀 卷第三十 持統紀 4年 단락157)