Advent, as we know it today, is a creation of the Western churches that looked to Rome as their leader. There were two main streams flowing into it. The first came out of France, during the fourth century AD, probably from Celtic monks. A period of about six weeks before Christ's Mass was used as a penitential and devotional period, a lesser Lent. The second stream came from Rome, where there was a practice of having a three-to-six week fast during which they had to come to church regularly. This was a fast before the feast of Christmas time.
The current form of Advent crystallized under Pope Gregory I, who set the current four-week length, and wrote liturgical materials for use in Advent. By the 10th century, the Celtic 'get ready' prayers and practices had been fully brought into the Roman form. Later on, the church adopted a system of liturgical colors, and Advent received a purple color not unlike Lent's. The 20th century brought a rediscovery of joy in Advent preparations. This was signaled among Protestants by using the color blue (with or without a touch of red in it). Some highly-Catholic areas hold special services on the nine days before Christmas (starting Dec. 16), as a worship novena.
Advent has fallen on hard times. For most people, it's become a time to get ready for whatever you're doing with family and friends on Christmas, and not a time to get ready for the Christ child. The bigger Christmas became, the more it swallowed up Advent. In fact, whatever Christmas-y thing we think of as being done before Christmas Day is actually done in Advent. In the US, everything after Thanksgiving is now seen as a part of Christmas. The main problem is not that Christmas intrudes on Advent. The real problem is that people no longer keep their Christmas focus on Christ, and then the Christ-less Christmas saps Christ from Advent. Practicing Advent as a religious season may help recover Christmas, but it can't do it by itself. If you don't look to Jesus every day in every season, you'll lose Advent, Christmas, Lent, and even Easter. It'll be a tiring rush, not a loving celebration, and it'll be about family or money or image and not our loving Maker. There are even some who openly advocate letting the world have its Christmas, and then Christians can do their own separate thing on Epiphany. (That would bring them nearly in synch with the old-calendar Orthodox.) But that, of course, chucks Advent as well as Christmas. Christmas is a day of joy, and much of what the non-Christian culture brings to the mix is joyous and fits well in a Christian context. Each Christian has as much right as anyone else to put their stamp on the public culture -- that's an important matter of freedom, and it needs to be exercised or it too will be lost.
