Africa's leaders meeting this week in Kampala to discuss the protection of displaced people should recognise that one of the root causes of conflict on the continent today is the denial of a right to a nationality - the right to be recognised as a person with rights and obligations in the state concerned. They should take steps to ensure that widespread discrimination in the grant of nationality ceases on the African continent.

Even in the poorest countries, a passport or identity card does not just provide the right to travel, but forms the basis of the right to almost everything else. People whose right to a nationality is denied may not have access to schools, health care, jobs - or the right to vote, hold a public position, or stand for office.

Ultimately, arbitrary discrimination in nationality law can be catastrophic. Political crises since independence in the Democratic Republic of Congo, Côte d'Ivoire, Zimbabwe, Mauritania, and other countries - including Uganda and Kenya - show the same pattern: economic collapse or outright conflict begins with the denial that one group of people are not 'really' nationals of the country (or the part of the country) where they have always lived.

As a fighter for the rebel 'new forces' in Côte d'Ivoire stated: 'We needed a war because we needed our identity cards'.

At minimum such discrimination results in unjust exclusion of millions of people from full participation in the political and economic life of the country they call home.

East Africa is not exempt from such problems. Uganda is one of the half dozen states in Africa whose law explicitly discriminates on the basis of race or ethnicity. In Kenya, people of Nubian or Somali origin find that they cannot obtain official papers of any kind (unless they pay well for the privilege). Though Tanzania has mostly been generous in the grant of nationality, and has benefited with social peace, Tanzanian governments have also used nationality law to try to prevent 'troublesome' individuals from speaking out or running for office by denying that they are citizens.

African states, like other states, are made up of people thrown together by historical circumstance. Africa's history of colonisation and land annexation lies behind many of the deepest nationality problems. It is not a coincidence that the countries where nationality has been most contentious are often the countries that saw the greatest colonial-era migration and land alienation. This pre-independence migration was not only of Europeans and Asians to the continent, but in even greater numbers of Africans within the continent. Injustices resulted from this history that have yet to be resolved, and those who benefited are still resented.

Today, however, it is the children, grandchildren and great-grandchildren of those who migrated who are still regarded as foreigners. Yet they are in the land of their birth and life-long residence and have no claim on the protection of any other state. Politically disenfranchised, it seems there is no demonstration of loyalty that can satisfy the requirements of the law.

If governments restrict the rights of some of those people to take part in national life by denying recognition of the nationality, history has shown that the consequences are disastrous. Though measures of affirmative action to address the injustices of the past are surely justified, a citizenship law based on a concept of ethnic or racial purity, or an essential link to the land, is not adapted to the reality of today's world.

Africa's leaders should thus take steps to adopt fair and non-discriminatory standards at continental level to govern the right to nationality, the very right belong to the state, on which so many other rights are founded. And they should urgently change the current rules at national level where they are not fair. They should follow their adoption this week of a continental treaty on the protection of the internally displaced with one that enshrines the right to a nationality.

Bronwen Manby is the author of two books on nationality law in Africa to be launched by the Open Society Institute in the margins of the AU Special Summit on Refugees, Returnees and Internally Displaced Persons (IDPs) in Kampala, Uganda October 22-23