Before conducting in-depth research, it is important to gather information you have about your topic and consider what you still need to know. This can include dates, places, terminology, and names of persons/entities involved in events or phenomenon you’re studying. Reference tools like dictionaries, encyclopedias, and handbooks are useful for this preliminary research phase.
World history : a comprehensive reference set by 
The Encyclopedia of World History by 
Events That Formed the Modern World by 
