Thousands of civilians started to pour back into the northern Syrian city of Manbij on Saturday, a day after the US-backed Syrian Defense Forces (SDF) recaptured the strategic transit point.

The sight of grateful civilians welcoming the SDF as liberators set a new tone in the fight against "Islamic State" (IS).

The Arab and Kurdish umbrella group liberated Manbij after a nearly two months of fighting that brought them over the Euphrates and deep into IS-controlled territory. The strategy was to cut off the Sunni extremist group's supply lines running from the Turkish border to IS's self-declared capital in Raqqa.

The success of the SDF offensive, backed by US airstrikes and Special Forces on the ground, gives new momentum to the anti-IS coalition. It also, again, enshrines the SDF as Washington's most capable partner on the ground.

"The partnership between US and SDF has reached a new milestone with the capture of Manbij," Mutlu Civiroglu, a Kurdish affairs analyst who is in regular contact with the SDF's military and political leadership, told DW.

Facts on the ground

Formed last year at US prodding, the bulk of the SDF is composed of the Syrian Kurdish YPG militia, but also includes Arab, Christian and Turkmen rebel factions that provide the force with greater legitimacy as it advances out of heavily Kurdish populated areas.

Parallel to its battlefield successes, the YPG's political wing, the PYD, has laid the groundwork for a Kurdish-dominated autonomous region. The Syrian Kurds have over the course of the five-year civil war bought their time and created facts on the ground.

Though no friends of the regime in Damascus, the Kurds have taken a so-called "third-position," taking sides neither with Assad nor Islamist rebel factions seeking his ouster. They are now in the unique position of being the only actors on the ground with relations with the regime, Russia and the United States. The combined military, political and territorial strengths gives the SDF a major bargaining chip in any political solution in the country.

Crossing redlines

The SDF's growing political and military clout is likely to further enrage neighboring Turkey, which views the YPG as a terrorist group because of its close relations with the Kurdistan Workers' Party (PKK) fighting in Turkey.

Ankara has repeatedly had its redlines crossed by the Syrian Kurds and the United States. The latest iteration is in Manbij, where first the SDF crossed the Euphrates, thereby crossing one "redline," then again when the YPG led the recapture of the city. This appears to have broken a reported understanding between Ankara and Washington that Arab forces would take the lead in Manbij.

Uniting the cantons

The Syrian Kurds' ultimate goal is to clear IS-controlled ground to the west of Manbij in order to unite their territories in the northeast, the so-called cantons of Kobani and Jazira, with Afrin.

"The SDF desires to go west to Afrin, which has been under political and economic embargo by the al Nusra Front and other Turkey supported groups for over two years," Civiroglu said.

Uniting the cantons would give the Kurds an uninterrupted stretch of territory along the Turkish border, a prospect that the Syrian regime and Russia could welcome, as it would also weaken the rebel groups they are fighting.

The question remains whether the United States will go along with an SDF offensive to unite the cantons and equally important, Turkey's response to the prospect of a contiguous Kurdish mini state on its border and what that would mean for any future political solution in the country.