The long battle for eastern Aleppo is virtually over. We all know its eventual outcome. It will take a few more days, perhaps weeks, for Syrian regime forces and their allies to overcome the rest of the embattled neighborhoods, or what is left of them. There will be more carnage as shell-shocked civilians attempt to flee to safer zones. Some will make it, others will not.

The casualty count includes children, women and the elderly, in what is already the biggest wholesale systematic destruction of an urban center since World War II. The extent of the humanitarian catastrophe has been exhaustively described and denounced by diplomats, journalists and humanitarian organizations. It is an understatement to say the world has done nothing to stop the massacre.

From a strategic point of view, the fall of eastern Aleppo will mark a major turning point in the Syrian crisis. It translates into the biggest defeat of the multifarious Syrian opposition groups and their equally diverse backers. By the same token, it will be the most important military achievement by the regime and its allies.

While US and European leaders insist that the outcome will not end the Syrian crisis and that a political solution remains the only plausible path forward, in reality the fall of Aleppo will embolden President Bashar Assad’s position and make it harder, if not impossible, for intermediaries to bring together representatives of the Syrian opposition and the regime to discuss a political roadmap. It is fair to say that the principles agreed upon in Geneva I, and what followed, have now become defunct.

While the Syrian opposition insists that it will not hand over what remains of the shrinking territory it still holds, it is logical to conclude that as the siege tightens it will have to accept a Russian offer to abandon the city. All the talk of a last-minute attempt by the US to provide a list of so-called moderate opposition groups will only delay the inevitable.

For Moscow and Damascus, all who remain in Aleppo are extremists with direct links to terrorist groups. If they are allowed to leave – that offer may no longer be valid in a few days – it will be to join other opposition fighters who have been evacuated to Idlib. It is in that governorate that the regime hopes to deliver a final and lethal blow to the opposition.

The fall of Aleppo may not spell the end of the Syrian uprising, as the regime is yet to extend its authority over much of the countryside, especially in the north, center and east, but the military challenge will be much less daunting.

By that time a new American president will be sworn in, ushering a new approach to Syria and other regional issues. Donald Trump’s take on Syria will be straightforward: To join forces with anyone who is willing to crush Daesh and other radical groups. That includes Russia, Turkey and even the Syrian regime. The subject of Assad’s removal will cease to become a priority or even a demand. That will be the price for a reset in US-Russian ties.

With most of Europe engulfed in a populist tide, Russian President Vladimir Putin will find more sympathetic listeners to his views on Syria and others. His nationalist agenda already intersects with the slogans of European far-right parties.

Aleppo may become a major milestone in the region’s shifting alliances. It signals an ongoing US pivot from a region that has been under its patronage for decades. Trump is being viewed largely as an isolationist, although his top Cabinet includes hardliners with an interventionist agenda. Equally, America’s retraction from the region will coincide with Russia’s resurgence as a key regional player, building alliances with countries such as Turkey, Iran, Egypt and Iraq.

Iran, which has invested money and men in defending the Syrian regime, will emerge as a winner as well, as it bolsters its Tehran-Baghdad-Damascus-Beirut axis. From now on, Assad will become a mere tool implementing Iran’s sectarian agenda. Its militias have leveled Sunni towns in Al-Anbar and elsewhere in Iraq, and now vow to march into Syria as well.

Despite the animosity between Ankara and Damascus, they may find themselves fighting for the same cause: Crushing Syria’s Kurdish hopes for autonomy and independence. That part of the miasmic Syrian quagmire will open a new battlefront, one that will extend for a long period of time and may metastasize to the rest of the region.

From early on, Syria’s popular uprising had turned into a costly proxy war, one that culminated in the seminal battle for Aleppo. Its fall will be a much bigger event than what most of the world would want to believe. It will trigger a wave that will deliver a new geopolitical structure of regional and local alliances, and will create a new set of key players. As the dust settles, a new arena of foes and friends will be emerging.

• Osama Al-Sharif is a journalist and political commentator based in Amman.