"Weekend is a late 19th century concept. You will find no referece to "weekend" in the
Federalist Papers. Sunday is a day of Christian Sabbath. In order to promote church attendance, we had "blue laws" for several centuries. The reason the "weekend" includes Saturday and Sunday rather than, say, Friday and Saturday, is one of Christian religious tradition.
I find you assertion that I am incorrect amusing because you really cite no countervaling evidence except for the silly idea of "weekend." I'm afraid I see nothing in your post to suggest that I should view you as an authority on this topic, merely pretentiously discourteous.
In cultures with a six-day workweek, the day of rest derives from the culture's main religious tradition: Friday (Muslim), Saturday (Jewish and Seventh-day Adventist), and Sunday (most Christian). However, numerous countries have adopted a two-day weekend over the past several decades, i.e. either Thursday–Friday, Friday–Saturday, or Saturday–Sunday.
In 1908, the first five-day workweek in the United States was instituted by a New England cotton mill so that [Jewish]] workers would not have to work on the Sabbath from sundown Friday to sundown Saturday.
https://en.wikipedia.org/wiki/Workweek_and_weekend