Ow do you account for the decline of the Holywood studio system between the late 1940s and the early 1960s?

Please do not change the title of the above essay as it is the one specified in my handbook. Sources used need to consist of textbooks, NOT just online sources as I can get penalised for this. If possible please use one or both of the following textbooks:

Hollows, Joanne (ed)
Approaches to Popular Film

Maltby, Richard
Hollywood Cinema (2nd edn)

Thank you.