Acontributing factors in the decline in both the tang and yuan dynasties was
failed military expeditions
weak leadership
corrupt government
the imposition of heavy taxes

the answer here would be

paul willis (born 1950) is a british social scientist known for his work in sociology and cultural studies. paul willis' work is widely read in the fields of sociology, anthropology, and education, his work emphasizing consumer culture, socialization, music, and popular culture. he was born in wolverhampton[1] and received his education at the university of cambridge and at the university of birmingham. he worked at centre for contemporary cultural studies and subsequently at the university of wolverhampton. he was a professor of social/cultural ethnography at keele university. in the autumn of 2010, he left keele university and is now a professor at princeton university.

paul willis’s work has focused mainly, but not exclusively, on the ethnographic study of lived cultural forms in a wide variety of contexts. from highly structured to weakly structured ones, willis examines how practices of `informal cultural production` to produce and construct cultural worlds `from below`.[2]

trained in literary criticism at cambridge,[2] paul willis received his phd in 1972 from the centre for contemporary cultural studies at birmingham university where he remained as senior research fellow until 1981. he gave a paper at the 9th symposium of the natiohnal deviancy conference in january 1972 entitled 'a motor-bike subculture

during the 1980`s willis served as youth policy adviser to wolverhampton borough council in the english midlands. there he produced the youth review (published by the council and ashgate) which formed the basis for youth policy and for the formation of the democratically elected youth council, both still functioning. during the 1990s he served first as head of the division of media, communications and cultural studies, and then as a member of the professoriate at the university of wolverhampton. in 2000 willis co-founded the sage journal, ethnography. in 2003 willis was hired as a head professor of social and cultural ethnography at keele university.