Why do US calendars put Sun. as the FIRST day of the week ?

Because Sunday is the first day of the week. The days of the week are based on older traditions including the Hebrew traditions. In the Bible, man was commanded to "remember the sabbath and keep it holy".The sabbath is Saturday, the seventh day of the week. Later Christian tradition began celebrating mass on the first day of the week, which is the day that Jesus rose from the dead (the Lords day), Sunday. The sabbath was a day of rest, not a day of worship. Over time, people confused the fact that we celebrated mass (and other religious services) on Sunday with the command in the Bible about the sabbath thus giving us questions like yours that are predicated on a mis-understanding of the traditions it is based on. To sum up, Sunday is the first day of the week, the Lords day, the day of worship, Saturday is the sabbath, the seventh day of the week, the day of rest. Sunday is not and never was the sabbath.

I don't care where the calendar put Sunday.

Monday is and always will be the first day of the week.

Because Sunday is the first day of the week.

Because that's how it is. In Greek which is my native language, Monday is Deftera which means second.

Because this is the first day of the wek for us. What is yoiur first day of the week?

Person who makes love under tree, have piece on earth !

Isn't it?

no one honestly cares!!!!!!!!!!!!!!!!!!!!!!!!!!!