It was another of those moments that will come back to haunt the United Nations. Just as its forces stood by during the Rwandan genocide of 1994 and in Bosnia’s Srebrenica massacre of 2005, so rebels of the M23 were allowed to walk into the eastern Congolese town of Goma unopposed.

The Congo is the UN’s largest peacekeeping operation in the world, with 19,000 troops and a budget of $1,402,278,300. At the time the town fell, the UN had 1,500 soldiers in Goma, backed by helicopters, artillery and tanks.

Despite having hit M23 with what the UN spokesman, Martin Nesirky, described as "hundreds" of rocket and missile rounds since the M23 attacks on the town began on 15 November, they were unable to prevent it being captured. Nesirky told journalists that the UN force was only there to support the Congolese army. When their poorly paid, ill disciplined troops broke and fled, the UN force commander on the ground decided to stand by as the rebels marched into town.

The real question is why the UN played such a passive role. Here the American position has been critical, particularly in stifling criticism of the Rwandan role in providing troops, weapons and ammunition to the M23. This has been extensively catalogued by UN experts. Their latest report (pdf) could hardly have been more explicit:

The Government of Rwanda continues to violate the arms embargo by providing direct military support to the M23 rebels, facilitating recruitment, encouraging and facilitating desertions from the armed forces of the Democratic Republic of the Congo, and providing arms, ammunition, intelligence and political advice. The de facto chain of command of M23 includes Gen. Bosco Ntaganda and culminates with the Minister of Defence of Rwanda, Gen. James Kabarebe.

Carina Tertsakian of Human Rights Watch told the New Statesman: “The US government has been surprisingly inactive and silent, despite the significant influence they have with the Rwandan government.”

Jason Sterns, a former UN investigator, lays the blame at the door of the Susan Rice, President Obama’s ambassador to the United Nations. Sterns argues that Rice has blocked criticism of the Rwandans. She “…has emerged as a holdout within American foreign policy, a sort of minority report to the prevailing criticism of Rwanda and the M23.” Rice prevented any explicit mention of Rwanda in the latest UN resolution on the Congolese crisis, leaving the text to call instead for “all relevant actors to use their influence on the M23 to bring about an end to attacks.”

Russia, France and – more recently – Britain have been developing a tougher line. This has finally begun to emerge. On 22 November William Hague and Justine Greening put out a joint Foreign Office–DFID press release.

"We judge the overall body of evidence of Rwandan involvement with M23 in the DRC to be credible and compelling,” they said. “We will be studying the implications of this report in full, but these allegations will necessarily be a key factor in future aid decisions to the Government of Rwanda.” That decision is said to be close to being announced, and could leave Rwanda without British funding – the largest source of foreign aid the country has enjoyed.

Officially, Rwanda, Congo and the Congolese are in agreement on the threat posed by the M23. On 21 November the three presidents met in the Ugandan capital, Kampala. A joint declaration was signed, calling for the M23 to leave Goma.

This was followed by a meeting of the Conference of the Great Lakes, three days later, again in Kampala. This brought together a wider group of leaders, including the presidents of Angola, Tanzania and Kenya. But on this occasion, significantly, Rwanda’s Paul Kagama was absent. The heads of state again called for the M23 to pull back 20 kilometres from Goma within two days, to allow the deployment of UN peacekeepers and a ‘neutral force.’

If, as the UN group of experts and many others believe, Rwanda, and to a lesser extent Uganda, are behind the M23, what is their long term goal?

This is less than clear, but there are indications that President Paul Kagame has the long-term objective of establishing a buffer state along his western border. Such a state would prevent any further threat from the defeated Hutu Rwandan army that fled into Congo at the end of the Rwandan genocide. They remain an armed presence in the region, in the form of the FDLR.

There are suggestions that Rwanda plans to establish a "République des Volcans" in the area. This – it is claimed – would be an extension of an ancient Hima-Tutsi empire. Both Paul Kagame of Rwanda and Uganda’s Yoweri Museveni have been portrayed as descendents of this tradition in the past – accusations they have denied.

Certainly it will require an immense effort for anyone to gain control over the Kivus. They are, today, held by a myriad of rebel movements, which fight for the control of the gold, cassiterite, coltan, wolfram, timber and diamonds to be found in profusion. Nor would the step necessarily receive the support of the Tutsi community in eastern Congo – the Banyamulenge.

The inability of the UN to hold Goma and the failure of Congolese government forces in the face of M23 attacks has taken a terrible toll on the local population. Christina Corbett, in Goma for Oxfam, says 140,000 have been displaced by this round of fighting alone. “We are very concerned that human rights violations – including forced labour, rape and illegal taxation – are taking place so regularly; they are not even being reported any more,” she says.

But international attention is scarcely concentrated on Congo. The fighting in Syria and Israeli attacks on Gaza are always more pressing concerns – even though the numbers of killed, injured and displaced are invariably many times higher. Central Africa is likely to remain a cauldron of conflict for many years to come.