Gregory Johnsen:

Well, the U.S. — for the offensive on Hodeidah, the U.S. has essentially giving the United Arab Emirates what one official called a blinking yellow light. That is, proceed, but with caution.

This is different from what the U.S. has done over the past couple of years, when the U.S. has put the brakes on any offensive going into Hodeidah. Hodeidah has been a target for the United Arab Emirates, for the Saudi-led coalition, for the Yemeni government for a number of years.

What's changed now is, last December, the former Yemeni president, Ali Abdullah Saleh, a man who ruled the country for more than three decades, he had allied himself with the Houthis. That alliance collapsed in four bloody days of a gun battle in the capital of Sanaa.

Saleh's nephew survived that battle. And he has flipped sides. And he's joined the government and he's joined the Emiratis and the Saudis. And his troops are pushing up the Red Sea coast toward Hodeidah. And the Houthis are moving back in front of him.

And so that offensive is one of the reasons that they're going in now, along with the U.S. yellow light.