Mr. Sunshine made me read and find stuffs. Lol. Some random links (more in comments):

• American Marines sent to Korea to protect their Legation since late 1800s 🔗https://books.google.com.my/books?id=TZFt9MoNar0C&pg=PA52&dq=marine+guards+american+legation+korea&source=gbs_selected_pages&cad=2#v=onepage&q=marine%20guards%20american%20legation%20korea&f=false

6
2