The United Nations has called the war in Yemen the world’s worst humanitarian crisis. An intermittent blockade by the Saudis and their partners in the United Arab Emirates has pushed as many as 12 million people to the brink of starvation, killing some 85,000 children, according to aid groups.

Led by Crown Prince Mohammed bin Salman, the Saudis say they are battling to rescue Yemen from a hostile faction backed by Iran. But to do it, the Saudis have used their vast oil wealth to outsource the war, mainly by hiring what Sudanese soldiers say are tens of thousands of desperate survivors of the conflict in Darfur to fight, many of them children.

At any time for nearly four years as many as 14,000 Sudanese militiamen have been fighting in Yemen in tandem with the local militia aligned with the Saudis, according to several Sudanese fighters who have returned and Sudanese lawmakers who are attempting to track it. Hundreds, at least, have died there.

Almost all the Sudanese fighters appear to come from the battle-scarred and impoverished region of Darfur, where some 300,000 people were killed and 1.2 million displaced during a dozen years of conflict over diminishing arable land and other scarce resources.

Most belong to the paramilitary Rapid Support Forces, a tribal militia previously known as the Janjaweed. They were blamed for the systematic rape of women and girls, indiscriminate killing and other war crimes during Darfur’s conflict, and veterans involved in those horrors are now leading their deployment to Yemen — albeit in a more formal and structured campaign.