The unity in diversity of the United States is one of the country's greatest strengths.

For my generation, coming of age at the height of the Cold War, fear of nuclear winter seemed the leading existential threat on the horizon. But the danger posed by war to all humanity-and to our planet-is at least matched by climate change.

Nuclear disarmament is the only sane path to a safer world.

You are already leaders. Your ideas, your actions and your decisions make a difference. More than any other generation, you have a voice. Social networking is changing how we interact - and it can change our world. You are in touch with peers from around the world. You understand the power of instant communication. I appeal to you to use that power for the common good, the power of communication and the power of networking.

On this International Day, let us promise to make peace not just a priority, but a passion. Let us pledge to do more, wherever we are in whatever way we can, to make every day a day of peace.

The taking of life is too absolute, too irreversible, for one human being to inflict on another, even when backed by legal process. Where the death penalty persists, conditions for those awaiting execution are often horrifying, leading to aggravated suffering.

We hold the future in our hands, together, we must ensure that our grandchildren will not have to ask why we failed to do the right thing, and let them suffer the consequences.