The Syrian army and its militia allies from the Shia world are preparing a counter-offensive to cut the recently-opened corridor connecting East Aleppo to rebel territory. Syrian and Russian aircraft pound the ruins of this corner of Aleppo through which also runs the main supply road to the government-held west side of the city.

The strengths and weaknesses of all sides in the Syrian war are on show in the present battle. First there was a victory by President Bashar al-Assad’s forces, which cut the enemy’s supply line to East Aleppo on 28 July. But this was balanced within a few days by a rebel success in another part of the city, which shows how equally the two sides are balanced. Claims of decisive victories in local offensives dribble away because neither side can keep up the momentum after initial advances. Each side has a limited number of effective combat soldiers of which they cannot afford to lose too many. The rebels are reported to have lost 500 individuals in their recent offensive.

Each side responds to any setback on the battlefield by asking and getting greater support from foreign backers. In this case, the Syrian government is looking to Russia, Iran and Shia militias from Lebanon and Iraq for reinforcements and air strikes. As they have shown repeatedly since 2011, none of these allies can afford to see Assad defeated and have a great deal riding on his staying in power. They were caught by surprise on 1 August when the rebel umbrella group Jaish al-Fatah, of which the main fighting component is the salafi-jihadi al-Nusra Front, broke through government lines in south west Aleppo. Rebel fighters, numbering between 5,000 and 10,000 men, are supported by Saudi Arabia, Qatar and Turkey. The Syrian army, battered by suicide bombers, retreated and their commander has been sacked.

UN pushes for pause in fighting as battle for Aleppo ramps up

We have seen this before. The Syrian army has enough combat troops to launch successful offensives backed by airstrikes. But it does not have the manpower to hold fixed position, often manned by soldiers who do little aside from manning checkpoints, harassing civilians and keeping out of danger. This has been a feature of the war since 2012: it is striking how few military units one sees on the roads or even in the front line. This makes each side vulnerable to surprise attack.

Pro-Assad forces are reported to have been reinforced by 2,000 fighters from Lebanese Hezbollah and the Iraqi Shia militias – their military experience, training and morale often making them superior to the regular army. If these units backed by heavy airstrikes cannot regain the small but crucial piece of territory lost earlier this month, it will show that the Assad government is weaker than was thought, but it does not mean that it is anywhere near defeat.

The stalemate in the war is demonstrated by the fact that both East Aleppo and government-held West Aleppo are now under siege. Water supplies are scant and little food can get in from the outside. UNICEF said on 11th August that “two million people in Aleppo are left with no access to running water as fighting intensifies.” Nobody quite knows how many people remain in Aleppo, but there are probably around 250,000 in the rebel half of the city and the rest on the government side.

It is striking how little real change there has been on the ground in western Syria since the end of 2012. This contrasts with the vast but under-populated spaces of eastern Syria where Isis and later the Syrian Kurds have made sweeping advances.

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A further factor reinforcing the stalemate in the war is that much of the fighting in Iraq and Syria is conducted on all aides by criminalised warlords with no interest in the well-being or even survival of the civilian population. But such cynicism, while usually realistic, can also be deceptive because it fosters a belief that nobody has a core of firm believers who will fight to the end.

Every fight in Syria takes place in political, sectarian, ethnic and social landscapes so distinct that they falsify generalisations about the course of the conflict. Fabrice Balanche of the Washington Institute for Near East Policy makes the point that “in Aleppo, the major divide between rebels and pro-government factions is not based on sectarian opposition – except for the pro-government Christian minority – but mainly on social class divisions and the historic urban-rural cleavage. Therefore, the chances for an anti-Assad uprising in western Aleppo are non-existent. If the rebels want to conquer the government-held portion of Aleppo, it will be with a hard fight.”

But Balanche remarks that any siege of East Aleppo by the government will be more difficult and prolonged than the eighteen month-long siege of the Old City of Homs. This was held by about one thousand rebel fighters occupying half a square mile of shattered buildings, while in East Aleppo there are an estimated 10,000 rebel fighters holding eight square miles. Moreover, “Aleppo is located in an Arab Sunni area very hostile to the Assad regime” while in Homs the surrounding rural areas were mostly loyal to the regime because they were Christian, Alawite or Shiah and because Hezbollah was able to close the border with Lebanon.

Indigenous factions in Syria are not going to bring an end to the war except by victory on the battlefield and this is a long way off. But the conflict has become progressively internationalised with the US starting its air campaign against Islamic State in September 2014 and Russia doing the same in defence of Assad a year later. Could the geopolitical environment be turning against the rebels after a rapprochement between Russia and Turkey? Turkish support or tolerance has always been crucial for the rebel cause. The meeting between Turkish President Recep Tayyip Erdogan and Vladimir Putin on 9 August sparked speculation that Turkey might do a U-turn in Syria, reconcile itself to Assad staying in power and abandon its anti-Assad rebel protégés.

It is not very likely. It is true that Turkey’s policy in Syria since 2011 has been a disaster. It has failed to displace Assad and establish a Sunni regime, but it has opened the door to a Syrian Kurdish de facto state ruled by the local branch of the Kurdistan Workers Party (PKK) against whom Ankara has been fighting a guerrilla war since 1984. Worse, the Syrian Kurds are the main military ally of the US in Syria.