Kabul, Afghanistan - The first day of January isn't celebrated as the beginning of the year in Afghanistan, but since the American invasion, it's become a new kind of holiday - a de facto birthday for thousands of Afghans who don't know when they were born.

During protracted wars in the 1980s and '90s, the government didn't have a system in place to register births. Because identification cards and driver's licenses weren't standard in this impoverished nation, families saw no reason to record the exact dates. Government paperwork asked only for an approximate birthday on the Islamic calendar.

But when the United States and its NATO allies arrived, they brought with them a flurry of job opportunities, visa applications and websites that all required a specific birthday on the Roman calendar.

"Those of us who don't know when we were born selected January first," said a U.S. Army interpreter named Tariq, who first wrote the date on his job application with the military and would repeat it when he applied for a visa, and whenever anyone asked. "It was very easy to remember."

Like many Afghans, Tariq, who requested that his last name not be used to avoid Taliban threats, has only a vague sense of his birthday, which coincided with the country's collapse into civil war in the early 90s.

As Internet access became more widespread, with 3G networks advertised in the country's major cities, the question of birthdays arose with even greater frequency. Urban Afghans were quick to create accounts on Facebook, Twitter and Gmail, all of which ask for the registrant's date of birth.

"In two days, it's every Afghan's birthday," Mohammad Hassanzai, an Afghan living in London, tweeted on Dec. 30.

Some worry that the lack of official birth registration - a problem that persists today, particularly in rural parts of the country - could have serious implications.

"Birth registration is instrumental in safeguarding other human rights because it provides the official 'proof' of a child's existence," said a 2007 United Nations report on the topic, which singled out Afghanistan.

Those records are helpful in reuniting families after conflicts or natural disasters, as well as helping children apply for refugee status. It also makes it easier to conduct a national census - an enormous challenge here.

"In Afghanistan, even though national legislation requires registration of children at birth, 23 years of conflict decimated both the administrative mechanisms and the social institutions that support them," the report said.

Afghanistan isn't the only war-torn nation whose citizens have chosen Jan. 1 as a makeshift birthday. In Vietnam, Somalia and Sudan, thousands wound up with the same birth date. In some cases, the State Department chose it for them. The department has bestowed that birthday upon more than 200,000 refugees since the Vietnam War, according to several estimates.

"These approximated birth dates allow the government to administer benefits and track and control immigration flow, but they lack both certainty and accuracy," wrote Ross Pearson in December in the Minnesota Law Review.

Afghans didn't wait to be assigned official birthdays. As U.S. immigration attorneys have accepted hundreds of visa applications, they noticed that many of their clients had already filled in their date of birth as Jan. 1. Many Afghans who are also unsure what year they were born offered their best guess on that line.

Most say they chose Jan. 1 because it was the easiest date to remember. But young Afghans in particular have coalesced proudly around it - a modern celebration that is also an implicit acknowledgment of their country's troubles.

The country's famous actors, such as Basir Mujahid, its athletes, such as cricket player Hasti Gul Abid, and its politicians, such as Mohammad Daud Daud, the former police chief of northern Afghanistan, all publicly celebrate their birthdays on Jan. 1.

Many Afghans, particularly the young, digitally savvy generation, remain curious about their true birthdays. But their parents don't offer much clarity, or at least enough to warrant a change.

"I'm not sure," said Hussain. "I think it was some time in the spring."