[quote=Omega]
Well the question is what happened 2340 years ago to change the calender?
[/quote]

We have a few very religious and very not religious nations here. I'm assuming, since calenders are often based off such things, that a religious figure died. Each of these nations would have seen it differently, but definitely an important part of history nonetheless. Like, athiest nations might see it as a cornerstone or turning point in the downfall organized religion, whereas religious nations might view it another, such as transcendence and what not.