The debate ended with a shock: The House of Commons defied Cameron’s call and rejected by 13 votes a planned campaign of British airstrikes. Chastened by the loss of its British ally from the fight, the United States soon pulled back from its own ambitions for military action, with President Obama punting the matter to Congress.

As Parliament debated again on Tuesday in an emergency session called as women and children were reportedly being shot dead in their homes by advancing Syrian government forces, the memory of that earlier vote loomed large in the Palace of Westminster.

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And it prompted two of Britain’s most prominent politicians to issue a particularly stinging charge: The tragedy of Aleppo, they told their fellow lawmakers, is partly your fault.

“We as a House of Commons, we as a country, we vacated that space into which Russia stepped, beginning its own bombing campaign on behalf of Assad,” said an unusually somber Boris Johnson, Britain’s foreign secretary, as he recalled the Aug. 29, 2013, vote.

Since then, Johnson said, “our ability to influence events in Syria or to protect civilians or compel the delivery of aid has been severely limited. The dictator was left to do his worst, along with his allies Russia and Iran, and the bloodiest tragedy of the 21st century has since unfolded.”

Johnson’s words echoed those of George Osborne, who had confronted his colleagues with a similar accusation earlier in the two-hour debate. Osborne, Britain’s treasury chief at the time of the 2013 vote, called the Aleppo atrocities “the price of not intervening.”

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“The tragedy in Aleppo did not come out of a vacuum. It was created by a vacuum, a vacuum of Western leadership, of American leadership, British leadership,” he said.

The effect was not limited to Aleppo, Osborne said. Tens of thousands of deaths across Syria, the rise of the Islamic State militant group, the destabilization of Turkey and Jordan, and a refugee crisis that has fed extremist politics across Europe can all be traced to the 2013 vote, he told a hushed chamber.

“That is the price of not intervening,” said Osborne, who lost his job as chancellor of the exchequer in the tumult that followed Britain’s June Brexit vote but remains a member of Parliament.

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Today, Osborne said, “it is impossible to intervene anywhere.”

Tuesday’s debate was the latest in an agonized reckoning for Britain over the price of intervention — and nonintervention — that dates to the country’s decision to join the United States in its 2003 invasion of Iraq.

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That choice — now widely regretted among British politicians and the public — was a significant factor in Parliament’s decision to reject intervention 10 years later in Syria. It also helped to delay Britain’s entry in a U.S.-led air campaign against the Islamic State in Iraq and Syria.

The emergency debate on Tuesday came about as a result of calls from members of the opposition Labour Party for the Conservative government to do more to protect Aleppo’s civilians.

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But even Labour politicians admitted that their party bore responsibility for allowing the situation in Syria to so badly deteriorate. It was Labour’s opposition to the 2013 vote that cemented its defeat. John Woodcock, a Labour lawmaker, said he felt “sick” when he thought of the party’s role in blocking British military action three years ago.

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Tuesday’s debate — like the one in 2013 — ended with Britain remaining on the sidelines.

Britain’s ability to influence events on the ground, Johnson acknowledged, was extremely limited. Aid drops, he said, would not work without Russian consent because British transport planes could be shot down.

The most he said he could do was call for Russia to withdraw its backing for Assad — an oft-repeated demand that has virtually no chance of being met given that Russia and Assad are now so clearly in command.

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“We are doing everything we can within the constraints that we face,” Johnson said. “I hope that Russia will see sense and join with us to secure the transition away from Assad. That is the only hope for a peaceful Syria. It’s up to them. It’s up to the Russians, it’s up to Iran. They have the future of Syria in their hands.”