Once again, the apparently insoluble struggle between Israel and Palestine has flared up before flickering into uneasy standoff. As usual, world leaders issued fierce warnings, diplomats flew in and the media flooded the region to cover the mayhem as both sides spewed out the empty cliches of conflict. After eight days of fighting, nearly 160 people lay dead.

Meanwhile, 2,300 miles further south, events took a sharp turn for the worse in another interminable regional war. This one also involves survivors of genocide ruthlessly focused on securing their future at any cost. But the resulting conflict is far bloodier, far more brutal, far more devastating, far more destructive – yet it gains scarcely a glance from the rest of the world.

Such is the cycle of despair in the Democratic Republic of the Congo – scene of massacres, of mass rape, of children forced to fight, of families fleeing in fear again and again, so many sordid events that rarely make the headlines. It can seem a conflict of crushing complexity rooted in thorny issues of identity and race, involving murderous militias with an alphabet of acronyms and savagely exploited by grasping outsiders. But consider one simple fact: right now, there is the risk of another round breaking out in the deadliest conflict since the Second World War.

If you missed the fleeting news reports, a rebel army of 1,500 men waltzed into Goma, a city of one million people, on Tuesday. In doing so, they humiliated not just the useless Congolese government but also the hapless blue helmets of the biggest United Nations peacekeeping mission, costing nearly £1bn a year. There are so many peacekeepers and development agencies in Goma it has become a boom town, home to some of the most expensive housing in Africa. Yet again, all these people proved impotent.

The leaders of this insurgent force, the M23, have declared their aim to march across this vast country to capture the capital, Kinshasa. Since it is backed by Rwanda and Uganda, which used proxy armies to do this once before in 1997, such threats cannot be dismissed. Joseph Kabila, the Congolese president, who, through fear of a coup, corruption and incompetence, castrated his own military, is reported to have responded by asking Angola to send troops to save him.

It is all a dismal echo of the Great African War, which officially ended in 2003 but dribbled on for another five years. This began when Rwanda and Uganda invaded in 1998, saw 11 countries from Angola to Zimbabwe involved and left more than five million dead and millions more displaced. There were war crimes on all sides as armies brutalised those unfortunate people living above the fabulous seams of minerals that fuelled the fighting.

It is hard to fathom the real aims of M23, formed earlier this year by mutinous Congolese Tutsi army officers. It could be they hope the Kabila government will implode or it may be they wish to create an independent state in the east of the country. One thing is clear: the international community needs to take tough and urgent action to stop a festering sore from poisoning a huge chunk of Africa once again.

The west bears some responsibility for the latest act in the Congolese tragedy. Not just because the ethnic divisions that cause such fear were inflamed during dark years of Belgian misrule. Nor simply because we gobble up those minerals that fund the warlords. But because at the heart of the horror in a country the size of western Europe is the tiny nation of Rwanda, darling of western donors seeking to assuage their guilt over inaction during its own genocide.

Britain and America in particular have lionised a regime guilty of ghastly internal repression and gruesome foreign adventurism, with catastrophic consequences for millions of Congolese. Admirers of Paul Kagame, the despotic Rwandan president, praise his country's economic development, ignoring that it is part-financed by trade in minerals plundered and pillaged from a ravaged neighbour. As far back as 2001, a Congolese rebel leader admitted such theft was Rwandan state policy.

Meanwhile, the west ignored repeated war crimes committed by this regime. The first invasion, originally to drive out Hutu genocidaires who fled over the Congo border and were allowed to regroup by aid organisations, led to an estimated 300,000 deaths of innocent refugees. One expert called this a genocide of attrition. The second invasion sparked even worse carnage. UN and human rights investigators reported how Rwandan troops and their allies slaughtered children, women and elderly people, often with the crudest weapons such as knives, ropes and stones.

Yet western leaders hailed Kagame as the modern face of Africa and pumped vast aid into his arms. Britain is the biggest bilateral donor; we directly funded agencies of repression, then led moves for Rwanda to join the Commonwealth. The links between our two countries are alarmingly close: Andrew Mitchell, our former aid minister, invited me last year to meet Rwanda's head of intelligence, a regular visitor to his Whitehall office. Meanwhile, Tony Blair advises Kagame on "governance", even while swanning around seeking peace in the Middle East.

Kagame angrily denies any involvement in the Congolese unrest. He always does, but the evidence is too strong to ignore. The report by UN investigators tying Rwandan military officials to the revolt insisted on five independent witness accounts before including information; their findings were endorsed by human rights groups and journalists. Yet again, the stories of abuse by their allies are revolting: the youngest recorded rape victim is eight years old, while a pregnant woman aged 25 was shot dead resisting rape.

After weeks of prevarication, Britain has finally admitted evidence of Rwandan support for M23 was "credible". Now we must make up for supporting this monstrous regime by cutting all aid, imposing tough sanctions and seeking war crimes proceedings against Kagame and his senior officials. The UN needs to review its peacekeeping mandate in Congo. Rwanda is set to join the UN Security Council in January, even as fears grow it may end up with a pliable client state carved out in eastern Congo.

Rwanda is far from the only villain in this drama. Uganda, another western ally, is also linked again to the latest unrest, the president's own brother accused of backing the M23. But Rwanda is the cause of much of the trouble. The truth is that six times as many people have died already in the Congolese wars as died in the Rwandan genocide. Time to say never again – or does the blood of Congo not count?