It was a major turning point in Syria’s long war.

For five years, U.S. policy relied on collaborating with a Kurdish-led militia both to fight the Islamic State and to limit the influence of Iran and Russia. On Sunday, U.S. leverage appeared all but gone.

What’s next: The deal opens the door for the Syrian military to return to the country’s northeast for the first time in years to try to repel a Turkish invasion.

On the ground: Amid the chaos of the ground invasion and strikes, hundreds of Islamic State sympathizers escaped from a low-security detention camp in the region. And the fate of other prisoners is unclear. U.S. Special Forces officers told our reporters they felt ashamed to abandon allies, while Kurdish fighters described feeling betrayed.

Impact: The fighting has caused the deaths of dozens of civilians and has forced over 130,000 from their homes, according to the U.N. The U.S. is planning to impose economic sanctions on Turkey.

Big picture: Turkey’s invasion upended a fragile peace in northern Syria and has already begun to unleash sectarian bloodshed. It also risks enabling a resurgence of the Islamic State, undoing hard-won gains against the group.