It’s pretty crazy how England stuck to the Julian calendar for like 170 years after it was obvious to every astronomer who knew his head from his rear end that it was off the mark. Queen Elizabeth and her scientific advisors supposedly wanted to go along with the Gregorian calendar in 1582, but the “Church of England” cried foul... on the theory that it would look like they were obeying the pope... and they bloody well couldn’t have that, could they? So the matter was quietly shelved for a century and half.
There are no religious wars. All wars are fought for political reasons. Religion is just one of the wardrobe departments. The topic can do without sectarian turmoil.
The change from Julian to Gregorian happened at different times, not even counting the various conquests of regions with large non-Christian populations.
http://www.searchforancestors.com/utility/gregorian.html