1. why does the chinese exclusion act mark a “watershed” in us history?

The Chinese Exclusion Act was a United States federal law.  It was one of the most significant restrictions on free immigration in US history, prohibiting all immigration of Chinese laborers.Act made permanent in 1902.  It was the first law implemented to prevent a specific ethnic group from immigrating to the United States.

At that time, Chinese laborers were very helpful for the United States, as it was period of construction, many cities (formation of Western US), in that condition, when the foreign laborers banned, their progress went down, so it marked as a "Watershed" in the US history

Hope this helps!

Gun but i don’t know for sure