In the English speaking world, as far as I am aware, Sunday is the first day of the week. This can be seen in calendars such as this one and in the default setting of the Excel "Weekday" function.

In Germany (and probably most of Europe as far as I know) Monday is considered the first day of the week. This can be seen in this calendar layout. It is also the ISO standard as can be seen here.

Given that in the bible, Sunday was the first day and Saturday the seventh, I assume that this convention was the earliest and that many countries later changed it to Monday (the first working day in the week) for some reason. Is this true, and if so, when and why did this change happen?