Is there a historical explanation as to why calling a chinese person "Chinaman" is considered more offensive than calling someone "Scotsman", "Irishman" and "Frenchman"?

by Solid_SHALASHASKA
SylkoZakurra

Adding to the question, to be the same wouldn’t it be Irelandman, Franceman, and Scotlandman? Why wouldn’t we say Chineseman?