Why does the New Year start on January 1?

Several countries around the world have already entered 2025, while in other nations, January 1, the first day of the year, will begin the moment the clock strikes midnight under the local time zone. Britannica states that during his reign, Roman emperor Numa Pompilius revised the Roman republican calendar to make January the year's first month instead of March. However, after Rome fell in the 5th century CE, several Christian countries modified the calendar to make it more reflective of their religion, leading to March 25 and December 25 becoming common New Year's Days. The Gregorian calendar, which restored January 1 as the New Year's Day, was immediately adopted by Italy, France, Spain and a few other nations.