The killing was on a terribly efficient scale, much of it accomplished not with bullets but machetes. It was 100 days of frenzied violence and merciless killing that left more than 800,000 Rwandans dead, the world struggling to comprehend, and the international community disastrously slow to act.

It was in the days before the internet and the world was slow to learn let alone comprehend the extent of the violence. World Vision staff from Australia and elsewhere were among the first to penetrate Rwanda’s borders in the days after the genocide started. The stories and images they captured flashed around the world, providing some of the first concrete evidence of the horrific scale and nature of the genocide.

"For 20 years these events have cast a dark shadow over the lives of Rwandans, with few families untouched by the atrocities. And yet, Rwanda today is a country of hope and growing prosperity."

In the year before the genocide began on 7th April, 1994, then president, a Hutu extremist, Juvenal Habyarimana, imported 500,000 extra machetes into the country. These simple, efficient farming tools proved even more effective as weapons as they were used ‘‘to hack hundreds to death or into a daze where they could only lie still, bleed out and expire’’, in the words of one witness.

Although they spoke Rwanda’s common language, the Tutsi who had grown up among their countrymen suddenly found themselves designated ‘‘cockroaches’’; parasites that needed to be purged. The incitement to rid the nation of every last Tutsi whipped so many ordinary people into a frenzy of killing and was propagated throughout Rwandan society – by its military, business, political and church leaders alike, turning neighbours against neighbours as entire families were wiped out by members of their own communities.

For 20 years these events have cast a dark shadow over the lives of Rwandans, with few families untouched by the atrocities. And yet, Rwanda today is a country of hope and growing prosperity.

Today, the survivors and perpetrators of the genocide begin 100 days of national mourning to commemorate the 20th anniversary of the explosion of violence – but also to celebrate the extraordinary achievements of their nation’s recovery.

Pronounced in the mid-1990s, after the genocide, a ‘‘nonviable’’ nation, Rwanda was recently described in the US journal Foreign Affairs as ‘‘one of Africa’s best-run, most orderly, least corrupt, and safest states, with a booming economy’’. Its gross domestic product has grown by an average of eight per cent in recent years.

Much is said in the media of the mixed blessing of the firm rule that the Rwanda Patriotic Front and its leader, President Paul Kagame, have instituted since seizing power and ending the genocide in 1994. It is often suggested, reluctantly, that this is the price that must be paid for the nation’s stability.

For his part Kagame has insisted the genocide must not be forgotten. Kigali’s haunting Genocide Museum has been established, along with other equally confronting memorials throughout the country. At Murambi, for instance, there is a graphic display of shrivelled corpses, the bodies of genocide victims that have been preserved to serve as an eternal reminder of the atrocities.

But I believe that the extraordinary progress Rwanda has made is equally due to the extraordinary decision that Rwandans have made to forgive each other and themselves. You don’t have to have been in the country very long before you realise that this is the choice that virtually every Rwandan has made – whether they are survivors, perpetrators or their descendants.

I met one such Rwandan recently. His name is Gaspard. Now 39-years-old, he was only 19 when he lost his parents and 10 siblings in the genocide. He quietly told me that he had chosen to forgive his Hutu school friend who had savagely killed some of his siblings. This perpetrator eventually confessed and was released from jail. This man took Gaspard and showed him the grave where he had dumped their bodies.

Gaspard also told me he had rebuilt his parent’s family home and has two young children of his own. Yes he remembers, but there is no trace of bitterness and he has embraced his family’s attackers. Gaspard, like most Rwandans, has taken to heart Desmond Tutu’s admonition: ‘‘There is no future without forgiveness".

World Vision has been working since the late-90s on reconciliation in Rwanda. This work proceeds from the startling proposition that forgiveness must come first; it must be offered before repentance or remorse. Only then does it have the power to reframe the future and allow the perpetrators to re-enter the community and not be permanently branded wrong-doers.

The decision to set up traditional village-based courts to deal with ordinary perpetrators willing to confess and express remorse - commanders and instigators faced the full power of the country’s formal courts - has greatly aided this process.

The entire country is now an unprecedented experiment in reconciliation as perpetrators and survivors build their lives side by side. Rwandans are committed to recovery and peacebuilding. Their journey has not been easy and it is far from over, but this is essentially a country transformed.

Yet there remains a larger question from the events of 20 years ago that should haunt us all. Does the international community even recall the lessons we all declared we had learnt from our tardy response to the genocide?

When asked this recently, President Kagame said: ‘‘I can give you a short answer: no.’’

These days we can, if we choose, be instantly aware of the latest developments in nations such as South Sudan, Central African Republic, the Democratic Republic of the Congo and Syria, which last week achieved the ignoble record of having generated a history-making one million registered refugees in neighbouring Lebanon. Yet this knowledge does not seem to have improved our ability to help these nations stop tearing themselves apart.

We condemn the loss of millions of lives, we provide relief aid and we build better refugee camps – but the conflicts continue. Somehow we must find a way to take the extraordinary story of Rwandans’ willingness to forgive each other for the sake of their nation’s future, and use this message of hope to end the suffering that so many still face every day.

Tim Costello is the chief executive of World Vision Australia.This article was first published in The Age.