The military operations that foreign states conducted in response to the Boxer Rebellion were the first coalition operations of the modern era.
"Coalition Coordination during the Boxer Rebellion: How Twenty-Seven “Councils of Senior Naval Commanders” Contributed to the Conduct of Operations,"
Naval War College Review: Vol. 71
, Article 8.
Available at: https://digital-commons.usnwc.edu/nwc-review/vol71/iss4/8