Boxer Rebellion: causes
Your problem may be just too many resources, so the task will be pointing the readers of your Guide to what they ought to be looking at, the best and most direct and most detailed stuff, perhaps. I expect that books and articles will be the main sources --AltaVista stuff seems often to be pretty superficial, but google.com seems to do better for this subject (see Fei Ch'i-hao's account).
Related Sites for 1900 Boxer Rebellion seems to offer quite a few links to resources that would be worth exploring a bit.