I'd first ask why would you need to? If this was for a history class, then you could give your view or teach them to research the topic, a fine time to learn how to use a library if they are old enough. If the topic is one you are knowledgable about you could have some conversations about the topic, looking into the causes and effects, if not then it is also a good time to learn together. Another trip to the library! Yes, I love the library and I think kids should get more exposure to it as a learning opportunity.
Bringing it up when its not necessary might be a bit much. It also depends on the age, maybe gloss over the general trend with a younger child or try to examine the cause and effect with an older one. There are lots of books, or even TV shows for different ages about historical settings that present the topics in age appropriate settings. I remember seeing many of the TV shows when I was young about kids time travelling to different periods, or a main cast of characters appearing in different time periods in stories; although they are rather dated by today's standards I am sure there are updated versions. Check out your local library!
Doing research on topics is both a learning experience for kids, asking them what they know about a subject is a good place to start, see what their interest is and try to tailor your response appropriately. Adding your own viewpoint is something every parent needs to decide, this goes for religion and politics as well, either you can bring up your child with your views only or give them yours and let them decide.