The Manchu were not Han, but they were Chinese in a broader sense: they've lived for centuries in what is now considered Chinese territory, and by the 19th century they were already assimilated to such an extent that most Manchus spoke Chinese, not Manchu. Today there are still ~10 million Manchus in China, but virtually none speak the language anymore. (Admittedly this is in part because in the early days of Communist China it was not a great idea to show any traces of potentially reactionary Manchu heritage.)
Manchu "foreignness" was a major contributor to the Taiping Rebellion, a war sufficient to kill something like 30 million people -- many more than were killed even in WW1. It was a big deal.
