US President Donald Trump’s December announcement that 2000 US troops stationed in Syria would withdraw within 30 days set off a wave of out-sized consequences.

It prompted the resignation of his Secretary of Defence, Jim Mattis, as well as his special envoy for the anti-ISIS coalition, Brett McGurk.

Senior US Republicans, such as Senator Lindsey Graham, were highly critical, urging Trump to reconsider his decision.

Australia and other US allies involved in the global anti-ISIS coalition were left scrambling for answers, trying to understand the implications for our own troop presence in the Middle East.

All this over a mere 2000 troops, a number far too small to affect the outcome of the civil war in Syria? As President Trump rightly said, when justifying his announcement, “Syria was lost long ago”.

After initially supporting the civilian uprising against the Ba’athist regime of Bashar al-Assad, the Obama Administration failed to provide much in the way of material support.

Since late 2015, the major external actors steering Syria’s fate have been Russia, Iran and Turkey. The interventions of Russia and Iran, in particular, have guaranteed the survival of the Assad regime, and slowly but surely helped it to re-conquer the country.

The only substantial parts of Syria that remain outside regime control are a rebel-held area around Idlib, and the Kurdish-controlled north-east of the country.

The United States and its western allies, not having the stomach for a broader role in the Syrian civil war, have instead restricted themselves to defeating ISIS in Iraq and Syria – a job which is, as President Trump said, now largely complete.

But though they are small in number, and their job largely done, the 2000 US troops in Syria have played a stabilising role far larger than their numbers would suggest.

First, they have provided protection to the Kurds, who have been a steadfast US ally in the Middle East and served as the spear-point for the re-capture of much territory from ISIS.

Turkey is deeply uncomfortable with the Kurdish enclave on its southern border inside Syria, seeing it as rallying point for its own Kurdish population, and has sent its military into Syria periodically to prevent the Kurds from capturing more territory.

With the protective trip-wire presence of the United States withdrawn, Turkey may now act more freely to dismantle the nascent Kurdish state in Syria. Indeed, so alarmed are they by this prospect, that the Kurds have requested that Assad send Syrian troops to help protect them from Turkey.

There are few peoples or nations in the Middle East more deserving of national self-determination and statehood than the Kurds: a people of 35 million who respect the rights of minorities, treat women as equals, eschew terrorism and anti-semitism, and have been a steadfast force for stability in the Middle East and western security partner for several decades.

That is why US abandonment of the Kurds would be not only destabilising for Syria, but wrong in principle.

Second, the presence of US troops in north-eastern Syria has prevented the realisation of a long-standing goal of Iranian policy: the establishment of a land bridge running from Iran, through Iraq and Syria, and into Lebanon and the Mediterranean Sea.

Iran already has a significant presence in Lebanon, in the form of Hezbollah; in Syria, through the presence of Iranian regulars and Quds Force fighters; and in Iraq, through Shiite militias funded and trained by Iran.

Until now the US presence in north-eastern Syria, especially near Al-Bukamal and the border with Iraq, has effectively prevented the creation of this land-bridge between centres of Iranian influence.

With US troops gone, the way will effectively be open for Iran to project power and transport missiles, weapons and militia from Tehran right through to the eastern Mediterranean.

This will significantly raise the risks of a conflict between Iran and the regional bloc of countries resisting Iran’s ambitions, notably Israel and Saudi Arabia. Israel and Iran have already clashed multiple times, usually over Syrian territory. If Iran seeks to take advantage of US withdrawal to funnel advanced weaponry and missiles to Hezbollah in Lebanon, expect a strong response from Israel.

And if Assad seeks to exploit US withdrawal to recapture the area around Idlib, expect Turkey – which has declared this issue a red line – to intervene.

Though the US presence has not prevented such clashes, it has stopped them getting out of hand. US retreat will cause the Middle East, not particularly stable now, to become a little more dangerous.

Lastly, the US withdrawal will further entrench Russia’s role as the region’s powerbroker and cement Assad’s diplomatic rehabilitation.

Arab states are already coming to terms with this fact, building ties with Russia and moving to re-admit Assad’s Syria as part of the Arab bloc.

Trump’s decision to withdraw US troops from Syria has caused such angst because it is of such geopolitical importance.

At stake is the future power order of the Middle East, and whether the US and its allies continue to play a role in shaping it.

The Trump Administration is now waking up to this fact.

The President has extended the timeline for withdrawal once already. And now US security adviser John Bolton seems to be laying out a conditions-based framework for withdrawal that could see US troops remain in Syria for the foreseeable future. It is a welcome reversal.