Really, American's think today is New Year's Day, but most of the people in the world don't. There are 5 times more people in China than the U.S., and their new year starts February 18th on our calendar. There are 4 times more people in India than here, and their year starts on March 22nd by our calendar.
Calendars are normally based on astronomical events, and the two most obvious astronomical objects are the sun and the moon.
The Islamic calendar is based on the motion of the moon, and their year has no connection with the motion of the earth around the sun. The Jewish and Hindu calendars combines both—years are linked to the motion of the earth around the sun, and months are linked to the motion of the moon. The Christian (Gregorian) calendar—the de facto international standard for civil purposes—is based on the motion of the earth around the sun, with no connection with the motion of the moon.
It's easy to think the world revolves around you, that everyone believes what you do. But that's not even true from one day to the next, calendar-wise.