MANBIJ, Syria.

For complicated reasons to do with war and politics, the only way in and out of the enclave controlled by Syria’s Kurds is on a rusty iron boat that ferries passengers across the Tigris River from Iraq. Late last year, photographer Alice Martins and I boarded one of those boats to head for the front lines in the fight against the Islamic State.

The journey took us more than 400 miles across the breadth of the newly emerging Kurdish region in northeastern Syria, a remote stretch of mostly desert land that covers as much as a third of the country.

Here, the Kurds have taken advantage of the chaos of Syria’s war to forge what amounts to a functioning state within a state that has collapsed in many other parts of the country. As they press ahead with their battle against the Islamic State, aided by the U.S. military, they are also expanding the frontiers of their region, to the west and the south, into lands that are traditionally Arab. The Kurds initially named their enclave Rojava, the Kurdish name for the area, but they have since renamed it the North Syria Federation, to reflect the new demography.