US President Donald Trump is locked in a legal battle to end the automatic right to citizenship for children who are born in the country even if their parents arrived illegally.

Roughly a third of countries have a similar concept embedded in their laws but debate is raging in many places over the right, known as "jus soli" or "right of soil".

- Widely used in the Americas -

Trump signed an executive order shortly after he took up the presidency in January to redefine the 14th Amendment to the US Constitution, which decrees that anyone born on US soil is a citizen.

The order has since been blocked by judges in lower district courts, and an appeals court upheld those rulings on Wednesday.

Trump had claimed that the United States, where the right was in force for more than 150 years, was the only country in the world to give birthright citizenship.

Yet on January 1, 2024 some 38 countries recognised the right of soil without imposing conditions, mainly on the American continent, according to data from the Global Citizenship Observatory at the European University Institute in Italy.

Newborns in the United States, Canada, Mexico, Argentina and Ecuador, also get citizenship in the country of their birth.

The right of soil in those countries goes back to the 19th century when they were breaking free of colonial rule and wanted to attract European immigrants.

"In the 19th century, the United States and emerging countries in Latin America had been emptied out by the massive decimation of the Amerindian population after the arrival of the Europeans in 1492," population expert Jean-Francois Mignot said.

Awarding citizenship to the children of immigrants at birth also helped create a sense of loyalty, he said.

Some countries in Latin America, like Colombia and the Dominican Republic, give the right of soil with exceptions linked to the place of residence of the parents.

- Game changing Benin -

In Africa, five countries have the right of soil -- Chad, Tanzania, Mozambique, Lesotho, and since 2022, Benin.

Maarten Vink, director of the Global Citizenship Observatory, said African countries would often use the citizenship rules handed to them by former colonial powers.

When Mozambique became independent from Portugal in 1975, Portuguese law on citizenship included an unconditional right of soil, which was then rolled back in 1981.

An absolute right of soil is also on the statute books in Tuvalu, Moldova, Bangladesh, and India and Pakistan.

In reality, Bangladesh and Pakistan do not apply the principle as systematically as other countries, Vink said.

- 'Double' right -

In total 33 countries, mainly in Western Europe and West Africa, apply a right of soil with conditions.

Belgium, France and Spain operate a "double right of soil", meaning a child born in the country to foreign parents gets nationality if at least one of them has also been born there.

In Belgium, the person must have been a resident for five of the past 10 years.

In France, a child born to foreign parents can get nationality from the age of 13, though it is not automatic -- they must apply and they must have lived at least five years in the country.