The Siege at Peking, by Peter Fleming
History in Three Keys, by Paul Cohen
The Siege of the Peking Embassy, 1900: Sir Claude MacDonald's Report on the Boxer Rebellion
Indiscreet Letters from Peking, by Putnam Weale
The Origins of the Boxer Uprising, by Paul Esherick
The Opium War, by Julia Lovell
And the ever-reliable:
Chinese Boxing