THE United Nations has rigorous and rarely met criteria for declaring a famine: 1 in 5 households in an affected area must be severely short of food; more than 30 percent of the population must be malnourished; and at least two starvation-related deaths must occur per day for every 10,000 members of the population.

U.N. authorities did not declare a famine zone anywhere in the world after 2011 - until this year. Now there is one in South Sudan, and soon there may be three more - in northern Nigeria, Somalia and Yemen. As many as 20 million people may face starvation.

This extraordinary emergency is attracting remarkably little attention, and alarmingly paltry funding. The U.N. Office for the Coordination of Humanitarian Affairs (OCHA) says $4.4 billion is needed by July to deliver food, water and medicine to afflicted areas, but only 10 percent of that sum has been raised.

If Congress allows the drastic cuts in U.S. foreign aid proposed by the Trump administration, the funds necessary to prevent mass starvation almost certainly will not materialize.

Last year, the United States provided almost a quarter of the World Food Program's budget, or about $2 billion.

The food shortage in Somalia, the site of the last U.N. famine declaration six years ago, is in part the result of a drought affecting much of East Africa. Tragically, however, the emergency in the other three countries is entirely man-made.

In South Sudan, government forces are impeding the delivery of food to two areas held by rebels, threatening 100,000 people with starvation.

In northern Nigeria, more than 5 million people are short of food in areas still controlled by the Boko Haram movement, which has aligned itself with al-Qaida.

In Yemen, 7.3 million people "urgently need food assistance," according to the OCHA website. There, the shortages result in part from the virtual closure of one of the country's largest ports, Hodeida, which supplies the capital of Sanaa.

The city is held by Houthi rebels; Saudi forces, which are attempting to drive out the Houthis, are slow to allow food shipments through a naval blockade.

The United States bears some responsibility for much of this chaos. It has backed the ill-advised Saudi military adventure in Yemen; the Trump administration recently resolved to step up support for the war while setting aside human rights considerations that caused the Obama administration to pause some aid.

The United States midwifed the birth of South Sudan, then failed to prevent its feuding political factions from going to war with each other. It has quietly waged war against the al-Qaida-linked al-Shabab movement in Somalia, through drones and proxies.

Staving off disaster will require speedy and decisive action. The United States should quickly supply its normal share of U.N. funding for food and push others to contribute. It should insist that Saudi and South Sudanese leaders open up the bottlenecks that are slowing food deliveries.

If the White House will not supply the necessary funds, Congress should step in. The United States must not stand by as millions starve this year.