Choose an event, the outcome, and the lesson that was learned. There are a number ways that you can go with this, but basically, this is a cause and effect question. What caused an event, what was the effect of the event, and why was the event significant? 
Be sure and choose an event/person/trajectory in history that is large enough to have a 2-3 page (500-750 word) analysis, including in-text citations and bibliography of works cited.