The most recent Sinicization I can think of, that of the Qing dynasty and the wider Manchu ethnicity, occurred from the late 17th century on, as Manchus living in China were assimilated into their environment while the Manchu homeland directly adjoining China was opened up to all kinds of influences.(句子来源：quora)

疑问：

1. that of the Qing dynasty and the wider Manchu ethnicity 是什么成分？

2. 本句中的 as 是“因为”的意思么？

3. 第二句用 as 引导一个句子和 while 引导一个句子这是不对的吧？