LONDON — A lot has changed in Ethiopia since hundreds of thousands of people died in the famine of the mid-1980s. Rates of undernourishment have plummeted in the past 25 years, child mortality is down by two-thirds and 90 percent of children go to primary school.

Now, the country whose name was once a byword for hunger is part of a global effort to end it entirely. Around the world, nations as varied as Brazil, Cambodia, Iran and the Philippines have reported progress toward the goals of the Zero Hunger Challenge, a campaign that the United Nations began in 2012.

The campaign’s ambitious target of eradicating hunger, experts say, helps lend structure and clarity to efforts to ensure that even the very poorest have enough to eat and to make food systems more resilient in the face of climate change, droughts, floods and other pressures.

Zero Hunger “is a challenge and it’s a hope,” said Danielle Nierenberg, president of Food Tank, a research and advocacy organization in New Orleans. “It gives us a concrete framework so we can get to a situation where everyone is well fed. I think that’s a realizable goal over the next 50 years.”

The goal is more complex than it may sound, however. The biggest challenge, experts say, is not simply for the world as a whole to produce enough food, though the pressures of a warming climate and a growing global population are likely to make that more difficult.

Ending hunger has more to do with making sure that the poorest have the means to buy or grow enough to keep their families well nourished and that infrastructure is strong enough and markets sufficiently robust to get food to where it needs to be, the experts say.

And it is about more than just filling bellies. Deficiencies in micronutrients like vitamins and iron, especially in the first years of life, stunt development and leave children with permanent physical and cognitive deficits. The World Health Organization estimates, for example, that as many 500,000 children go blind every year because of vitamin A deficiency, and half of them eventually die.