Complex sentence: Meanwhile both Japanese civilian and Chinese civilians and media in mainland, Hong Kong and Taiwan welcomed the leak citing their rights to know, and each group viewed the content of the video as presenting evidence favorable to their own cause in the dispute.
Split into simpler sentences: Meanwhile both Japanese civilians and Chinese civilians and media in mainland China, Hong Kong and Taiwan welcomed the leak citing their right to know. Each group viewed the content of the video as presenting evidence favorable to their own cause in the dispute.