poor orientals built your railroads for shitty wage.
and they didn't burn your city down.
EDIT: i don't think orientals sold slaves. Africans sold slaves, since they were too busy enslaving each other. It was part of their lifestyle. Rich Africans owned hundreds of slaves and built harem of beautiful black women to show their power and shit. hell, enslaving other tribe was great. You remove competition and at the same time you arm yourself with the greatest invention of mankind: Gun powder.
Europeans didn't even have a proper means to transport slaves through Pacific Ocean. Pacific Ocean was too turbulent and too fucking long. West American continent wasn't colonized enough or even surveyed by 1700s to mid 1700s when slave trade started to slow down and shit. With no railway, no means of fast transportation, it makes good economic sense to go after African slaves. And it made good economic and political sense for Africans to go after other tribes and sell them to Europeans.
I dunno if China would have sold their subjects as slaves though. They did exchange a number of eunuch and Chosun gave hundreds of their women as tribute to China. Chinese thought whites are fucking barbarians and shit. even Koreans, who adopted to their confucius system to the core (Chosun was, and remained to be until Sino-Japanese War, greatest and most loyal vassal to Ming/Qing Dynasty), Chinese called them "cooked barbarians." Chinese were racist as fuck.