However, this work has faced regular setbacks. The end of the civil war in Sri Lanka in 2009 led to tens of thousands of deaths and a systemic failure by the UN to speak up and act. For more than three years, the international community has remained divided over the response to the situation in Syria, providing only a fraction of the necessary humanitarian funding while fuelling the fire with arms to both sides in the mistaken belief in a military solution.

The world needs to overcome these moral blind spots. UN member states may have rival definitions of national interest, or be unwilling to take on new financial or military commitments. They may be daunted by complexity and risk, or concerned that discussions about an imminent crisis in other countries might one day focus on their own situations. But the results of this indifference and indecisiveness are clear: the bloodshed of innocents, shattered societies, and leaders left to utter the words "never again", again and again - in itself is a sign of continuing failure.

Over the past decade, the Central African Republic has struggled for global awareness of its plight and, over the past year, suffered the collapse of the state, a descent into lawlessness, and gruesome mass killing that has instilled widespread terror and sparked an exodus. People are exploiting religious identity in the fight for political objectives, threatening a longstanding tradition of peaceful coexistence between Muslims and Christians.

I appeal to the international community to provide the military support urgently needed to save lives, get police back on the streets and enable people to return to their communities. The African Union and France have deployed troops, but efforts by the European Union to launch a force have so far come to naught. There is an equally pressing need to start a political process in which reconciliation figures prominently. Any further spread of violence may engulf the wider region.

When the collapse of a country is this profound, the challenge may seem insurmountable. Yet history proves otherwise. The sustained support of the international community has helped Sierra Leone and Timor-Leste make dramatic transformations. Rwanda has registered notable gains in development, and other countries have healed after unspeakable violence. The Central African Republic can walk the same path. I will continue to stand with the government in charting a course that can build a stable and prosperous country that its resources and traditions can make possible.

In Rwanda, I visited the genocide memorial and paid tribute to the victims - as I have for other tragedies that have challenged the world, from Auschwitz and Cambodia decades ago, to others in our time. The international community cannot claim to care about atrocity crimes and then shrink from the commitment of resources and will required to actually prevent them. Global leaders should do more to prevent the preventable, and to counter the cruelty taking place before our eyes. People everywhere should place themselves in the shoes of the vulnerable, from Syria to the Central African Republic, and ask themselves what more they can do to build a world of human rights and dignity for all.

Let us show people facing dire threats that they are not alone or abandoned - and that the lifeline they need is on its way.

The author is secretary-general of the United Nations.