The celebration of a new year has been around for about 4,000 years. Babylonians celebrated the new year during an 11 day feast beginning with the first new moon after the Vernal Equinox (first day of spring). Why then? Well, why not?
The beginning of spring is the logical time... the time of planting new crops, emergence of dormant perennials, and blossoms opening. January 1st on the other hand, has no agricultural nor astronomical significance. It's merely arbitrary.
The Romans continued to celebrate the New Year in late March but as various emperors fiddled with the calendar, the date soon became out of sync with the sun. When Julius Caesar established the Julian calendar in 46 BC, the New Year was established as January 1st. The Romans continued to celebrate with feasting throughout the first few centuries AD, but the Catholic Church condemned the celebrations as Pagan.
As Christianity became more widespread, the early Church began having its own religious celebration concurrent with many of the Pagan celebrations, including New Years and naturally there has been some overlap and mingling. Some Christian denominations still celebrate the day as the Feast of Christ's Circumcision.
It has only been in the last 400 years or so that the Western world has celebrated January 1st as the New Year's Holiday but many of the traditions have deep roots. The early Bablyonians started off the new year with a clean slate by returning borrowed tools. The Scots celebrate with what is called "First Foot" where they visit other homes, bringing gifts of food or coal.
I'll list some more current traditions in another post about New Year's Celebrations.