Why is the week for most countries, minus here in the US, start on a Monday. Which would make sunday the seventh day
It is fairly simple to show that the weekly cycle hasn't changed no matter what the calender says in some countries. There was a time where the date changed, but the weekely cycle was unchanged.
The shift went like this: Thursday October 4, 1582 followed by Friday October 15, 1582. This correction was the result of the Julian calender not being accurate so it was changed to the Gregorian.
Also, the present day Jews still worship on Saturday, the 7th day, and they have a history that goes all the way back to Christ. Sunday is thus named because it originated from pagan sun worship that was slowly incorporated in to Christianity about 300 years after Christ lived on earth.
Ingoring the issue of the belief being right or wrong, the Catholic church claims responsibility for the change. "We observe Sunday instead of Saturday because the Catholic Church, in the Council of Laodicea (A.D. 336), transferred the solemnity from Saturday to Sunday." - The Convert's Catechism of Catholic Doctrine (Reverand Peter Geiermann, C.S.R. of January 25, 1910.
Out of curiosity, when did the Morman church officially begin? It was after A.D. 336, correct?