Here are some strategies to help narrow your topic:
Aspect -- choose one lens through which to view the research problem, or look at just one facet of it.
Place -- generally, the smaller the geographic unit of analysis, the more narrow the focus.
Relationship -- ask yourself how do two or more different perspectives or variables relate to one another. Designing a study around the relationships between specific variables can help constrict the scope of analysis.
Time -- the shorter the time period of the study, the more narrow the focus.
Type -- focus your topic in terms of a specific type or class of people, places, or phenomena.
Cause -- focus your topic to just one cause for your topic.