1 million people have contracted cholera in Yemen. You should be outraged.

Even so, this number stands out: The International Committee of  the Red Cross reported today that 1 million Yemenis have contracted cholera in the past 18 months. More than 2,000 have died, according to the United Nations. It's the largest cholera outbreak in world history.

(In a statement, Yemen’s coalition government disputed the number, suggesting  that it was “exaggerated,” and noting that “it is nearly impossible to accurately determine whether the suspected cases are cholera or simple diarrhea.")

Let that sink in for a second. One million people have contracted a disease that we've understood how to treat and contain since John Snow sat by a water pump in 1854. For cholera to spread this fast, everything has to go wrong. In Yemen, everything has.

Cholera is a waterborne illness, spread when food or water comes in contact with waste from someone who already has the disease. It's easy to protect against — you're safe as long as you've got clean water to drink and a way to disinfect food — and it's easily treatable. All that's required is fluids. As David Sack of Johns Hopkins University put it to NPR: “A patient with cholera should never die.”

Yemen is on the brink of a horrible famine. Here’s how things got so bad.

Yemen is the poorest country in the Middle East and has one of the least hospitable climates. Much of the country is desert, and climate change has made it even harder to grow crops and access fresh water. Experts predict that Sanaa will be the first capital city to run out of water. Yemenis import more than 80 percent of their food, fuel and water.

Even so, before fighting broke out in 2015, there was no cholera in Yemen. The country's civil war changed all that.

The conflict started as slow-motion coup. Houthi rebels took over parts of the country; the government fought back. Saudi Arabia stepped in, offering assistance in the form of airstrikes that have killed thousands of civilians.

Today, the country has no functioning national government. Parts of the country are in the hands of the Islamic State militant group or other local actors. As Chatham House put it in a recent report, “Yemen resembles less a divided country than a collection of mini-states engaged in a complex intraregional conflict.”

Saudi Arabia lifted its blockade of Yemen. It’s not nearly enough to prevent a famine.

That conflict has made it much harder to move goods into the country. Saudi Arabia has enacted a blockade of water, air and land ports. Much of what does make it into the country is smuggled over various checkpoints, and Yemenis are forced to pay the price, an especially steep obstacle considering much of the population hasn't received a salary in months.

“Cholera has spread in the Houthi areas because of the blockade and bombing by the Saudi coalition, which has destroyed the public water and sanitation systems,” explained Daniel Varisco, a postdoctoral scholar at the Austrian Academy of Sciences. “It appears to mainly be a problem in urban areas due to the breakdown of the water systems.”

Yemen's outbreak began in October 2016 in Sanaa, with a handful of cases spreading to Aden and other cities. Two months later, cases had been reported in about 15 provinces. Six months later, about 320,000 people had contracted the disease.

The pace of infection slowed, but by April it had picked up again. By June, nearly 200,000 people had been infected, and UNICEF warned that Yemen was facing “the worst cholera outbreak in the world.” Nearly half of the infections struck children, who suffered a quarter of the deaths.

In response, the United Nations mobilized a large-scale humanitarian effort. Some 50 organizations delivered 900 health workers to the country, along with supplies and makeshift clinics. Even so, by last month, 900,000 people had contracted cholera.

Those who come down with the disease have few good options in Yemen. The nation's health system has collapsed, and most health workers haven't been paid in months. Fuel is scarce, making it nearly impossible to keep hospitals running. Aid groups have set up rehydration centers and clinics, but it's not nearly enough.

With so little infrastructure, even the most dramatic international campaigns can't get off the ground. Last spring, the World Health Organization mobilized to send 1 million cholera vaccines to Yemen. The plan was to get at least 500,000 doses into the country by the summer. By June, WHO had suspended the effort, rerouting the antidote to other high-risk countries. It was a decision made by the Yemen government, which feared that it wouldn't be able to treat citizens in areas controlled by Houthi rebels.

But scientists doubted that a vaccine campaign would be effective. “In an outbreak setting, the impact of [oral cholera vaccine] is greatest when used to protect communities that are not yet affected,” Tarik Jašarević, a WHO spokesperson in Geneva, told Science magazine. “There are few such areas in Yemen now.” By June, cholera had spread to all but one of Yemen’s 22 provinces.

There is some good news. The Red Cross says that the number of new cases has declined for 14 weeks. Experts say the infection has probably peaked.

But there are no guarantees. Sixteen million people lack reliable access to clean food and water. The disease could spike again in March, when the rainy season begins. Experts warn, too, that diseases kill more people, and more quickly, when a population is underfed. In Yemen, 1.8 million children are acutely malnourished. Nearly half a million babies and toddlers are starving.

To stem the disease, Johan Mooij of CARE told NPR, you need clean water. “If there's no fuel coming into the country to make the water pumps work, then people will have to go back to filthy water again,” he said. “That will make cholera increase again.”