Once you have selected an initial topic, the next step is to develop research questions. You'll do this by using probing questions, such as what, why, when, how, would/could, should.
Phrasing your topic in the form of questions helps direct the research process. For example, with a topic of "During the Jim Crow era, the Negro League had a profound influence on American politics, culture, social and recreation", the following questions may be asked:
WHAT questions focus on a particular aspect of the topic: What were the major impacts of the Negro League on major league baseball and American society?
WHY questions ask for an explanation of something--why something happened, why it did not happen, or why one thing is better than another. Why did the Jim Crow era persist for so long?
WHEN questions focus on timing or history. When did the Jim Crow era occur?
WHERE questions focus the topic on a location, either geographical or other. Where did Negro League baseball have its most profound impacts (society, culture, baseball, economy)?
HOW questions focus aspects of the topic, on a process, or on the origin. How did African-Americans playing in the NL impact baseball and society?
WOULD / COULD questions focus on possibilities. Could the integration of African Americans have occurred sooner? What prevented this?
SHOULD questions focus on the appropriateness of a particular action, policy, procedure, or decision.
Source: Mike Palmquest. Bedford Researcher. Colorado State University.
A good research question will lead to your thesis statement.
For example, the question...
During the Jim Crow era, how did the Negro Leagues impact baseball and American society?
...might lead to the following thesis:
"During the Jim Crow era, the Negro League had a profound influence on American politics, culture, social and recreation."
Strong thesis statements
or "why should I care?" test
Source: Thesis Statements. George Mason University.