During a presidency often forced to focus on issues of national security, the fight against global disease was sometimes viewed as an anomaly or exception. It wasn't and isn't. America has a direct stake in the progress and hope of other nations.

Many of the world's problems - terrorist networks, criminal gangs, drug syndicates, pandemic diseases - are no more than a half-day plane ride from the United States. These challenges tend to take root in hopeless, poorly controlled areas. This does not mean that promoting health and development is a substitute for confronting immediate threats. It does mean that no national security strategy is complete in the long run without promoting global health, political freedom and economic progress.

Early in my first term, it became clear that much of sub-Saharan Africa was on the verge of catastrophe. In some nations perhaps a quarter of the population was infected with HIV. The disease was prevalent among teachers, nurses, factory workers, farmers, civil servants - the very people who make a society run. Drugs to treat the disease existed and were falling in price, but they could hardly be found in Africa. Whole countries were living in the shadow of death, making it difficult for them to plan or prepare for the future.

Our response began with an effort to reduce mother-to-child transmission of the virus - the saddest, most preventable aspect of the crisis. In 2002, America helped found the Global Fund to Fight AIDS, Tuberculosis and Malaria to encourage the concerted action of wealthy nations. In 2003, I announced the President's Emergency Plan for AIDS Relief (PEPFAR), an ambitious bilateral program to confront the worst of the pandemic with speed and urgency. Members of Congress from both parties, leaders of African nations and outside advocates such as Bono became partners with my administration in a tremendous undertaking.

In all of these efforts, my concern was results. I was frankly skeptical of some past foreign assistance programs. In this crisis, we needed not only more resources but also to use them differently. So we put in place a unified command structure; set clear, ambitious, measurable goals; insisted on accountability; and made sure that host governments took leadership and responsibility. The results came more quickly than many of us expected. Early in 2003, there were perhaps 50,000 people in sub-Saharan Africa on AIDS treatment. Today, thanks to America, other donor nations and the tireless work of Africans themselves, nearly 4 million are. Fragile nations have been stabilized, making progress possible in other areas of development.

But the most vivid results, for me, had a more human scale. On World AIDS Day in 2005, two young children from South Africa, Emily and Lewis, came for a White House visit. They chased around the Oval Office before Emily did what many others no doubt wanted to do - she fell asleep in her mother's lap during my speech. Both young children were HIV-positive but had begun treatment. I could not even imagine all that curiosity and energy still and silent.

I firmly believe it has served American interests to help prevent the collapse of portions of the African continent. But this effort has done something more: It has demonstrated American character and beliefs. America is a certain kind of country, dedicated to the inherent and equal dignity of human lives. It is this ideal - rooted in faith and our founding - that gives purpose to our power. When we have a chance to do the right thing, we take it.

On this World AIDS Day, considerable progress has been made. The United Nations recently reported that the world has begun to halt and reverse the spread of HIV/AIDS. However, considerable need remains. Every human life is precious, and far too many people around the world continue to suffer from the disease.

We still hope for an AIDS vaccine. In the meantime, there are millions on treatment who cannot be abandoned. And the progress in many African nations depends on the realistic hope of new patients gaining access to treatment. Why get tested if AIDS drugs are restricted to current patients? On AIDS, to stand still is to lose ground.

I am happily out of the political business. But I can offer some friendly advice to members of Congress, new and old. A thousand pressing issues come with each day. But there are only a few that you will want to talk about in retirement with your children. The continuing fight against global AIDS is something for which America will be remembered. And you will never regret the part you take.

The writer was the 43rd president of the United States.