Bloodied children. Maimed children. Children pulled from the rubble, grey with dust, their mouths and lungs clogged with sand. Children who have lost their mother, father or brother. And these are the survivors. Unicef issued a blank “statement” to express its outrage, saying it had run out of words. Eastern Ghouta’s suffering – after long years of besiegement and multiple chemical attacks, including 2013’s devastating use of sarin – has escalated again. In this horror, even one of those trapped there asks in disbelief: “Are we really alive? Do others know we actually exist, and that we’re alive in these basements?”

Less than a year ago, the opposition enclave on the outskirts of Damascus was declared a “safe zone” in a deal between Russia, Iran and Turkey. There are almost 400,000 people still trapped there. Seven hundred have died in recent months, but attacks this week have killed more than 250, according to the Syrian Observatory for Human Rights, and two dozen on Wednesday alone. Seven hospitals have reportedly been bombed since Monday and witnesses say barrel bombs are being used. This siege and bombardment do not constitute a war crime, but war crime upon war crime upon war crime.

The UN’s calls for a ceasefire are ignored. If anything, the situation is likely to worsen: “The offensive has not started yet. This is preliminary bombing,” a commander in the pro-Assad forces told Reuters. Syrians warn that this could be more brutal than the terrible siege of Aleppo. A doctor in eastern Ghouta compares it to Srebrenica, which once pressed the international community to a promise that it would never happen again. It did, and no one is even making such promises now.

It is not “out of control” violence, as some have suggested, but calculated and licensed violence. Beneath Bashar al-Assad’s rhetoric of destroying “terrorists” lies a raw realism: no one will stop him. “The strong do what they can and the weak suffer what they must,” Thucydides wrote in the fifth century BC, imagining Athenian justifications for the siege of Melos and the terrible price they exacted for the Melians’ resistance. War gave full rein to greed and ambition, ruthlessness and brutality, the historian believed – but also spawned them, degrading and warping moral standards and perpetuating further conflict.

In Syria, the original causes of this seven-year conflict have long since been subsumed by the interests of multiple players and the pursuit of profits in the war economy. The powerful are too invested to back out now, or pay heed to the Syrians destroyed by their ambitions. Eastern Ghouta, once the breadbasket of Damascus, is choked with dust and starving. The overlapping wars have stolen the lives of at least half a million Syrians and displaced half the population, forcing six million to flee abroad to a precarious life in which their suffering is met at best with an inadequate response and at worst with an utter lack of concern or hostility.

Even as eastern Ghouta suffered, two more developments highlighted the multiplying strands of this catastrophe and the fact that there is no end in sight. On Tuesday Turkish forces fired on a convoy of pro-regime forces entering the north-western Afrin region to support Kurdish fighters fending off Ankara’s offensive there. Meanwhile, Moscow has acknowledged that “several dozen” of its nationals and citizens of other former Soviet states were killed by a US-led coalition strike in Deir ez-Zor, eastern Syria, two weeks ago, having previously dismissed reports of mercenaries’ deaths as “classic disinformation”. It is realising – as the US did in Iraq – that crushing the opposition is not the same as winning, still less being able to effect an exit.

The US too has no expectation of departing, as the secretary of state has made clear. Israel is being drawn deeper into the mess as it faces an emboldened, entrenched Iran and seeks to keep “Syrian Hezbollah” militias away from the border. The unwieldy coalition created by the battle against Islamic State has collapsed with the disintegration of its caliphate; its fighters will remain a danger in Syria and further afield, but the various parties involved have returned to other enmities. As Thucydides warned, war has its own logic and trajectory. This tangled disaster continues to grow.