Yemen’s civil war has carved the country into battling factions. And now it’s virtually sealed off from the outside world, because of a blockade imposed by Saudi Arabia. This is Yemen’s main port and shipyard, now almost empty of containers. That means essential goods are not reaching a nation that relies almost entirely on imports for food, fuel and medicine. Eight million people, one-fourth of the population, are at risk of starvation. Here’s how a blockade compounds a crisis in a country already strangled by war. First, why is there a blockade? Yemen is essentially the battleground for a regional proxy war. On one side Is Yemen’s official government, backed by Saudi Arabia. On the other is a rebel group called the Houthis, backed by Iran. In November, Houthis fired a missile at the Saudi capital, Riyadh. The Saudis retaliated by imposing a total land, air, and sea blockade on Yemen. It effectively locked in 28 million people and locked out ... everything. The blockade was partly lifted to allow in humanitarian aid, but not commercial imports. But the vast majority of essential goods come in on commercial ships. So today, there isn’t nearly enough food or fuel coming in or going around. Where is the effect of the blockade most visible? Let’s look again at Yemen’s largest port, Hodeida. Around 80 percent of imports arrive through it. And two-thirds of the population live in the areas directly served by it. But because it’s in an area controlled by the rebels, the Saudis have it tightly controlled. A review of marine traffic shows the arrivals of ships in Hodeida dropped by half in November. And these satellite photos show an active shipyard one year ago, right before the blockade. And now, the port is almost empty. One key shipment not getting through Hodeida is fuel. Aid organizations we spoke to say the fuel shortage is setting off a vicious circle of suffering. These aid groups are warning of a reduced ability to deliver food and aid, reduced access to pumped and purified water, and a struggle to keep generators on at hospitals. Fuel prices have doubled since the start of December. Fuel is especially needed to deliver water across one of the driest countries on earth. Earlier this year water shortages triggered a cholera epidemic that affected nearly one million. And now, water is unaffordable for two-thirds of the country, prompting fears of other disease outbreaks. Yemen’s war is a humanitarian crisis. Is it also a crime? That’s what N.G.O.s and humanitarian groups are examining. It’s against the laws of war to restrict humanitarian assistance and destroy objects essential to survival. And using starvation as a method of warfare is also a war crime. What is the U.S.’s role in all of this? The U.S. isn’t directly striking Yemen. But it’s the main supplier of arms to Saudi Arabia. Yemenis have often found fragments of American-made munitions after deadly airstrikes. In a short statement this month, President Trump called on the Saudis to allow essential goods enter Yemen. It was a rare rebuke to a key ally. But for now, there appears to be no end in sight to the blockade — or the conflict.