By definition the weekend is the end of the week. People’s definition of the weekend may vary slightly but I think that most people would agree that includes most or all of Saturday and Sunday.
So why then do Americans insist on putting Sunday at the beginning of the week in calendars and diaries? It just seems to be another example of religiosity creeping in to American culture and dictating that Sunday should come first in the week because it is the holy day.
And once again, America just looks silly and goes by a convention that no one else in the world observes.