During Turkey's deadly military offensive against Kurdish-controlled parts of Syria, the situation on the ground was described by one US official as a "total shitstorm".

The chaos started with US President Donald Trump's abrupt decision to withdraw 2000 US troops from the border between Turkey and Syria on October 6, clearing the way for what the White House called a "long-planned" Turkish offensive and sending all the other parties in the conflict into a scramble of repositioning.

Amid the mayhem, the dozens of deaths and tens of thousands of displaced civilians, Trump pulled out his remaining 1000 troops on October 13, giving rise to the unedifying sight of incensed Kurds pelting departing US tanks with potatoes. Days later, as the scale of Turkey's onslaught became clear, Trump moved to punish Turkey, pausing negotiations over a $100-billion trade deal and doubling tariffs on imports of Turkish steel (while, in New York, US prosecutors went ahead with charging Turkey's Halkbank over a multibillion-dollar scheme to evade US sanctions against Iran) before US sanctions were then dropped following a ceasefire in the region.

The US-shaped hole in north-east Syria left a power vacuum now being filled by a range of players. Former allies are falling out. Bitter rivals are becoming friends. Syria (a US foe supported by Iran and Russia) and the Kurds (jilted US allies) have forged an uneasy alliance against the Turks.

Meanwhile by October 26,  hundreds of Russian military police, including from the southern Russian region of Chechnya, had joined Syrian border guards to "help" with the withdrawal of Kurdish forces and their weapons to 30 kilometres of the Syrian-Turkish border.

With all of these rifts and shifts, from small and large players, it is hard to keep up. Who are the groups behind the acronyms? And what do they all want?

What does Turkey want?

In dropping bombs on towns near its border with Syria, Turkey had two main goals: to ensure that its border with Syria was free of Kurdish forces, and to create a space inside Syria where as many as 2 million of the 3.6 million Syrian refugees currently living in Turkey can be resettled. This project is ongoing.

For years the government in Ankara, which controls the second-largest standing army in NATO after the United States, had been pushing Washington to jointly establish a "safe zone" extending 32 kilometres into Syrian territory, without success. President Erdogan had repeatedly warned that Turkey could take unilateral military action, after accusing the international community of failure to act. Cue the current situation.

Who are the Turkish-backed rebels?

As Turkey continued its aerial bombardment, it was providing cover not only for its own ground forces but for rebel groups that it backed. Within six days of the US withdrawal, one of these groups, the Sunni Islamist extremist Ahrar al-Sharqiya, had been blamed for executions, including that of Kurdish politician and women's rights activist Hevrin Khalaf. She and her driver were forced off the M4 highway by machine-gun fire, savagely beaten and shot dead.

The existence of such groups has been a while in the making.

Since the war in Syria began in 2011, militant opposition to the Syrian President Bashar al-Assad and his regime has splintered into a bewildering array of competing groups, including jihadist elements such as Islamic State and what was al-Qaeda's force in the region, which has been rebranded several times and is now known as Jabhat Fatah al-Sham – and is active in the region now.

At first, the West backed the broadly secular and nationalistic Free Syrian Army (FSA) in its fight against Assad's regime but, as the war dragged on and Russia intervened, the FSA lost Western support and began to splinter. In 2016, when Ankara decided to send ground forces into Syria as part of Operation Euphrates Shield, Turkey took the FSA brand and applied it to a collection of militias. These rebels against the Syrian regime now rely on Turkey for sponsorship – and on displaced Syrian populations within Turkey for manpower.

Turkey calls this force the Syrian National Army (SNA).

Some of those fighting in the SNA will resent the Kurds for their failure to join the fight against the Syrian regime and for attempting to carve out a separate state; others will be from families displaced from northern Syria in earlier rounds of fighting who see this as an opportunity to pay back the Kurds.

What do the Kurds want in Syria?

The Kurds are a mainly Muslim ethnic group distinct from the Arabs, Persians and Turks. They make up about 15 per cent of the Syrian population. Across the region, in the territory of the modern states of Armenia, Iran, Iraq, Turkey and Syria, Kurds form an "invisible nation" of between 25 and 40 million, according to estimates by the CIA Factbook.

When the Ottoman Empire was defeated in World War I, the Allies initially envisioned a referendum for populations in eastern Anatolia that might have resulted in the creation of a Kurdish state. Turkish nationalists, led by Mustafa Kemal "Ataturk", launched a war of independence that overthrew the Ottoman authorities and secured the borders of the modern Turkish republic, extinguishing Kurdish hopes of independence.

After Iraq's defeat in the Gulf War of 1991, Britain, France and the United States created a no-fly zone in the north of Iraq to protect the country's Kurdish population. This zone became an autonomous region, in effect, and its existence was formally recognised as part of the national structure of Iraq after Saddam Hussein's overthrow in 2003.

The Kurds have many different political groups and attendant militias spread across the region. The Kurdistan Workers' Party, or PKK, has been fighting for autonomy in eastern Turkey for three decades, carrying out bombings and other assaults that have seen it listed as a terrorist organisation in Turkey, the United States, the European Union and Australia. Turkey's government regards the main Kurdish force in Syria – the People's Protection Units, or YPG – as an arm of the PKK.

In 2015, the YPG became the lead force in a US-backed coalition of Syrian militias known as the Syrian Democratic Forces, or SDF.

When the civil war in Syria began, Syrian Kurds avoided direct confrontation with the Assad regime, choosing to concentrate on building an alternative authority in Kurdish-populated territory along Syria's northern border.

Over time this authority began to characterise itself as a semi-state called "Rojava". The Syrian regime did not attempt to reassert its rule in Rojava, focusing its stretched forces on combating other rebel groups. By fighting alongside the West to eject Islamic State from northern and eastern Syria, the Kurds had hoped they would gain international recognition for Rojava as an autonomous entity.

What is the Syrian government doing?

The civil war in Syria dramatically weakened the power and influence of Bashar al-Assad. While backing from Iran and Lebanon's Hezbollah prevented his overthrow, his effective rule dwindled to metropolitan and coastal areas in the country's west, as territory held by rebels and the Islamic State's "caliphate" grew.

Now that the Kurds have turned to him in desperation, he will hope to regain the north-east and east of the country …

Two factors turned the war back in his favour: international intervention against IS and Russian deployment against other rebel forces. Assad has repeatedly vowed to liberate every inch of Syrian territory, and has regained many major centres in the north and south of the country once held by rebels.

Some analysts believe Assad will reach an understanding with Turkey over a partition of territory in the north, quietly encouraged by his Russian patrons.

The regime has brutally punished any perceived opponents in places it already took over, including Homs and Aleppo, The Washington Post reported. In the north-east, many local activists worked with the Kurdish SDF, which is now working with the regime. Their lives may now be at risk.

How does Islamic State fit in?

Trump cited the defeat of Islamic State and the dismantling of its territorial "caliphate" by US and Kurdish forces as justifying his decision to get troops out of Syria's north. Yet many US officials have warned that IS is not destroyed but merely dormant, including in the form of sleeper cells, and the current mayhem will allow it to regroup.

About a dozen Australians are among the 2000 to 8000 former IS fighters in prisons that had been run by Kurdish forces in the region. There are also 65 Australian women and children among about 75,000 or more families of IS fighters in camps, including the biggest, al-Hawl. Even before the current conflict, the Red Cross described conditions there as "apocalyptic".

In other areas, some IS fighters have walked free. It was reported that five captives had escaped as Turkey bombarded a Kurdish-run prison in Qamishli on October 11, for example. And nearly a thousand fighters and sympathisers fled a camp in Ain Issa on October 15, The New York Times reported. The situation, said one Kurdish commander, was "an unbelievable mess".

Trump had said that the United States had taken the worst IS detainees out of Syria to ensure they would not escape but the US military took custody of only two British detainees, half of a cell dubbed the Beatles who tortured and killed Western hostages.

Why is Russia there?

It was Russia's intervention with air power in 2015 that helped turn the tide of Syria's civil war in Assad's favour and Trump's decision to pull out of the north-east has cemented Moscow's central role in shaping the country's future.

Russia helped broker the new alliance between the Kurds, who were forced to compromise or face a potential bloodbath, and the Syrian regime against the Turks.

In their role as "peacekeepers", Russian military police moved into the town of Manbij as US forces pulled out. US vehicles and weapons appeared to have been removed at one outpost but a Game Boy, a refrigerator full of soft drinks and what appeared to be a few boxes of Krispy Kreme donuts remained, according to videos posted by Russian soldiers and journalists who toured the place.

US officials said they had "deconflicted" with their Russian counterparts as they withdrew.

In a deal struck between Turkey and Russia, from October 29 their joint forces will start to patrol a narrower, 10-kilometre strip of land on the Syrian side of the border where US troops had been deployed for years alongside their former Kurdish allies.

Russia warned that if Kurdish YPG forces did not withdraw from the border region they would be crushed by Turkey's armed forces.

with agencies