Complex sentence: Following his time in South Korea, Wu became China's ambassador to Japan, serving from July 2001 until August 2004; he returned to China to take up his post as Vice Minister of Foreign affairs at the end of that assignment.
Split into simpler sentences: Following his time in South Korea, Wu became China's ambassador to Japan in 2001. He returned to China to take up his post as Vice Minister of Foreign affairs at the end of that assignment.