In some countries, whenever someone applies for a Ph.D. admission, the universities ask for a research proposal. A research proposal includes a literature review and bibliography.
If the research is paper-based research, i.e. no popular survey or experiment is involved, I see no further need for research work. For instance, say, someone wants to redefine and redescribe the origin and purpose of British colonialism in India. In this case, if the researcher has already read the needed resources and done his desk-research, the only task left is writing a thesis that may take at most three months.
What is the difference between preparing a research proposal and writing the actual thesis in the case of theoretical research?