Currently we are studying WWII- and just finished WWI. (Our history schedule does go along with Classical Conversations.) One resource I have found helpful, and you may too, is The World Wars, An Introduction to the First & Second World Wars by Usborne Books.
This book is packed full of information and engaging photos. My daughter has really enjoyed reading it.
We often use the library as a resource for books on subjects we are studying, but given this is a topic we study for several weeks (and will in future years as well), I decided to purchase the book.
If Usborne still publishes this book, I am unaware. I found my copy on Ebay.