Until she graduated from high school, Sonia Camilise never had reason to question her nationality. She was born here in the Dominican Republic and grew up speaking Spanish, dancing merengue, and watching the boys play baseball in the grassy lot outside her family's small house.

"I am Dominican," she says. "Of course."

But two years ago, when she went to get a certified copy of her birth certificate – a necessary part of the college application process here – she discovered that her government had a different perspective.

The civil registry officers told her that she was not Dominican, but Haitian. Their reasoning: Ms. Camilise did not have the papers to show that her father, a Haitian immigrant, had legal residency here when she was born.

It was a shock, she says. In the Dominican Republic, citizens need new copies of their birth certificates for everything from enrolling in university to getting a visa to acquiring a marriage certificate. Now her government was essentially rejecting her – part of a new policy that Dominican officials say is necessary to combat illegal immigration.

But Haiti doesn't accept Camilise, either. Yes, she arguably looks Haitian, with her dark skin; and yes, she lives in a batey, a neighborhood built for Haitian sugar cane workers – such as her maternal grandfather – who migrated across the island of Hispaniola in the 1950s and '60s. Yet Camilise has never been to Haiti. She has a Dominican birth certificate and national ID, and even her mother was born in the Dominican Republic. She doesn't speak Creole or French, the languages of Haiti. According to Haitian officials, whose laws say that people who have chosen other nationalities cannot be Haitian, Camilise is obviously Dominican.

And so, she is stuck. She's unable to go to university or land a job legally, unable to even get a passport that would let her leave the country and try somewhere else. She is, in the lingo of human rights activists and international organizations, "stateless."

• • •

Although the details differ from case to case, Camilise is far from alone in her predicament. The United Nations estimates that nearly 12 million people around the world are stateless.

Statelessness has nudged in alongside better-known issues such as access to clean water, refugee rights, and education as a top priority on the global humanitarian agenda of the United Nations, governments, and advocacy groups.

International advocacy groups have different motives for the new focus on a problem first identified in the aftermath of World War II. Some, including the Soros Foundation's Open Society Institute, became conscious of the issue after the Sept. 11 attacks, when they started looking at how noncitizens were affected by the so-called war on terror. Other organizations began focusing on statelessness as part of a broader intellectual trend of exploring the powers and limits of the nation-state – the same trend that has led to international criminal courts. And although many of those involved with statelessness say that a half century after the problem was identified as a global predicament it is still widely ignored and misunderstood, they also say that they see attention beginning to snowball.

"People who are stateless really have no life," says Maureen Lynch, the senior advocate for statelessness initiatives at Refugees International, an organization at the forefront of raising awareness about the problem. "To be a stateless person – it's like you are standing still and the world moves on around you.... It leads to a variety of human insecurity – for individuals, for communities, for society."

The stateless live in all parts of the globe, from Europe to Southeast Asia to the Caribbean – and even in the United States. And while the historical facts of stateless groups vary, the growing human rights movement is sounding the alarm over what advocates see as the universal impact of the condition: impoverishment, conflict, lack of education, poor health care, and other violations of human rights. If the state is the instrument that protects and ensures rights, they explain, those who live without a nationality are completely vulnerable.

Earlier this year, the UN Refugee Agency (UNHCR) announced that it was "redoubling" its efforts to combat statelessness, saying the predicament "impacts not only the individuals concerned but also society as a whole, in particular because excluding an entire sector of the population may create social tension and significantly impair efforts to promote economic aid and social development."

Since 2007, the State Department has included a section on statelessness in its annual country reports, meaning it judges other nations' human rights records, in part, by how they handle citizenship rights.

Some individual countries have also taken steps to reduce statelessness within their borders. Although there are still barriers to citizenship, Nepal, for instance, recently provided documentation to hundreds of thousands of people – some of the millions who had been unable to obtain citizenship rights because of a change in law requiring people to prove "Nepali origin," a phrase that was applied differently in different regions and did not consider a mother's nationality. Bangladesh has started extending citizenship to some of the Bihari people, who for years have been rejected by both Pakistan and Bangladesh – a casualty of the division between East and West Pakistan in 1971. In May, the US Senate Judiciary Committee held hearings on a bill that would help the 4,000 or so stateless people within the US, suggesting new mechanisms for them to acquire green cards.

"The good news," Ms. Lynch says, "is that statelessness is a problem that can be ended."

It may be difficult to find one blanket approach, she says, but in many cases, adjustments in laws and bureaucratic policy will fix much of the problem.

• • •

In Europe, the Roma – also known derisively as gypsies – often lack identity documents. In Kenya, according to Human Rights Watch, more than 100,000 ethnic Nubians, whose forebears were brought there from Sudan by British colonialists in the late 19th and early 20th centuries to act as soldiers, have long been denied Kenyan citizenship. Although the situation is starting to change, Nubians cannot acquire identity documents or work in the formal sector, and inhabit large swaths of some of Nairobi's poorest slums.

In Kuwait, the government denies citizenship to what Refugees International estimate to be 120,000 bidun people (descendants of nomadic Bedouins who either didn't claim or weren't granted citizenship at the time national borders were drawn); in Syria, approximately 300,000 Kurds do not have citizenship. Palestinians are perhaps the best-known stateless group.

In the US, many of the estimated 4,000 stateless are failed asylum seekers or were visiting the US when their home country collapsed, according to Senate staffers who have worked on the issue. For instance, in testimony to the Judiciary Committee, Refugees International president Dan Glickman told of a woman from the former Soviet Union who no longer had a home embassy or consulate, and could not meet residency requirements to become a Ukrainian or a Russian citizen. She'd applied unsuccessfully for asylum in the US before the collapse of the Soviet bloc, but now had nowhere to return. He said she lives in constant fear of being jailed.

"Stateless people are perhaps even more vulnerable than refugees due to their near-total lack of ability to exercise their human rights," he said.

Sometimes their situations do overlap with refugee crises. During the 1990s, for instance, human rights groups estimate that around 250,000 Rohingya Muslims who had been denied citizenship in Burma (Myanmar) fled to Bangladesh because of the struggles they faced as noncitizens.

But most stateless people are not refugees, officials with the UN say.

The exact percentage is difficult to calculate, however, because the statistics about stateless people are sketchy at best.

UNHCR is the international body charged with addressing the predicament of stateless people. It collects data on statelessness from individual governments – some of which have valid statistics, but others of which UN officials privately acknowledge are highly inaccurate. "Mapping" statelessness – gathering statistics on not only how many people lack any citizenship, but also on their regions, the reasons for their statelessness and their family histories – is a key part of UNHCR's new strategy of increasing its effort to focus on stateless people.

"We need to undertake a more systematic effort to address this frequently ignored issue," said Volker Türk, director of UNHCR's division of international protection, when the agency announced its new statelessness effort in March. "There is growing interest among states, including donors and civil society, and this creates new opportunities for UNHCR to implement its mandate."

The concept of statelessness first attracted widespread international attention in the aftermath of World War II, when the population of Europe was in flux. The experience of the Jews, who had been denationalized by Germany's Nuremberg laws, along with the postwar border shifting, prompted the UN General Assembly to include the right to nationality in its 1948 Universal Declaration of Human Rights.

More proclamations followed. In 1954, the UN adopted the Convention Related to the Status of Stateless Persons, which attempted to outline rights for those who had no fixed nationality. Seven years later, the UN adopted the Convention on the Reduction of Statelessness, which took measures such as allowing nationality to pass from mother to child, and forbidding countries in most cases from denationalizing citizens. It also charged the UNHCR with overseeing the issue of statelessness.

But these conventions carried little weight, and the attention fizzled. Only 33 countries ratified the 1961 convention.

It was a tricky issue. No country wants to give up the power to decide who should be a citizen, those working with statelessness acknowledge; in many ways, the ability to exclude people, to draw lines between "us" and "them," is at the heart of the concept of the nation-state.

"In many ways, nationality is the last bastion of the sovereign state doctrine," says James Goldston, executive director of the Open Society Institute's Justice Initiative, which now focuses on statelessness as one of its main advocacy issues. "Article 15 of the Universal Declaration of Human Rights says that everyone has the right to nationality, but nowhere does it say which state must secure that right. We still need some greater clarification of states' obligations."

The question is compounded, he says, by the different histories and characteristics of stateless people; at face value, the Palestinians, say, have little in common with the Dominicans of Haitian descent, or the hill tribes of northern Thailand.

"One of the great challenges in terms of advocacy is that these people are dispersed," Mr. Goldston says. "And it does manifest itself in different ways all across the globe. It is hard to mobilize the stateless as one class or group."

• • •

The Dominican Republic shows the hyperlocal aspect of the question, as well as the common threads of marginalization.

Here, the issue of statelessness revolves around the complicated and troubled relationship between the Dominican Republic and its much poorer neighbor, Haiti. The history of these two countries, which share the island of Hispaniola, is fraught. The Dominican Republic celebrates its independence from Haiti; Haitians remember how Dominican dictator Rafael Trujillo massacred thousands of their countrymen living along the border in 1937. [Editor's note: The original version of this story stated 30,000 Haitians were killed. Historic accounts vary between 4,000 and 35,000.]

Today, the Dominican government estimates that hundreds of thousands of Haitian immigrants enter their country illegally each year – with concerns that the number is increasing dramatically since January's devastating earthquake in Port-au-Prince. At the same time, the Dominican economy depends on cheap – many say, ill-treated – Haitian labor to fuel the sugar, tourist, and construction industries. Haitians and Haitian descendents who live in the Dominican Republic often talk about severe racism and mistreatment; Dominicans talk about how Haitians take jobs and tap already strained public resources.

"To understand the Dominican Republic's actions, you have to imagine the American reaction if there were 30 million illegal Mexicans coming into the US every year [as opposed to the Pew Hispanic Center's estimated 500,000]," says one UN worker, who asked not to be identified because her organization works with the government and the topic of statelessness is so sensitive.

Until this year, the Dominican Constitution said that a child was a Dominican citizen if he or she had Dominican parents, or was born on Dominican soil. There were two exceptions, however – the children of diplomats and the children of people "in transit."

For years, "in transit" meant someone docking in the country's port on a ship, or stopping for a few days' visit. But in the past decade, the courts have changed this description to include migrants – even those who came with valid work permits.

The government increasingly applies this standard retroactively, saying that some children and grandchildren of Haitians should not have gotten Dominican birth certificates in the first place. This year, the government passed a new Constitution that said children of illegal immigrants were not citizens.

The move is similar to what some activists and legislators in Arizona would like to see as an extension of the state's controversial new immigration laws – and a warning of how complicated such a stance can be.

Activists estimate that tens of thousands of people are finding themselves in Camilise's situation. And this, they say, has consequences for education (teenagers can't go to college), health care (already HIV rates in the bateyes are among the worst in the Western Hemisphere, and activists worry about "survival sex" and access to medicine), and poverty levels (without documents, a person can't be legally employed). Some also worry about an increase in human trafficking, prostitution, and other forms of exploitation.

"Citizenship rights are fundamental to being able to access everything," says Rachel Aicher of the Open Society Institute, who has worked on statelessness cases in the Dominican Republic. "State services are dependent on producing identification."

If you have no country, nobody is providing you services and nobody is protecting your rights.

In Batey Esperanza, a neighborhood about an hour's drive from the sprawling capital of Santo Domingo, almost every cinder-block house has a story about statelessness.

Yuly Paredes says he had to leave his semiprofessional baseball program because the Dominican government wouldn't give him a birth certificate, without which he would never get a contract with the American teams who scout here. Louis Michel, a 75-year-old who says he came here legally from Haiti to cut sugar cane in 1979, says his Dominican-born grandchildren are now unable to go to college. Altagracia José, who was born in the Dominican Republic, points to her teenage daughter, who is pregnant, and says that the girl had to leave school because she had no papers.

"You know what happens to a young girl who is pregnant – if she can't go to school, she gets a man," she says. "And then another man. And the boys, they have no future. They turn delinquent."

Ms. José says that now she, too, cannot get copies of her papers, which keeps her from obtaining legal employment.

"I cried when they told me I was not Dominican," she says.

"I cannot choose another country. I've never been to Haiti – I am no more Haitian than I am Puerto Rican, or American. If I am stateless, I am nobody."

• Travel for this article was funded by a grant from the Pulitzer Center on Crisis Reporting.