As you read books and articles you will probably encounter statistics. The sources below can help you locate additional statistics, everything from the population of London in 1780 to the amount of wheat grown in Nigeria.
For earlier years, prior to WWII, we have statistical compendiums in print:
Subject encyclopedias are good places to start on your exploration of a topic. They feature brief essays on historical themes, people, places, and events. The essays are similar in scope to Wikipedia entries, but are written by authorities in the field. They will guide you to key articles and books on your topic, and supply important names, dates, and terms that can help you make informed decisions as you progress with your research.
In addition to online reference databases, the library also has an extensive collection of print resources, far too many to list. If you are not finding what you need use the contact information on the left sidebar and ask for help!