The 21st century will overturn many of our basic assumptions about economic life. The 20th century saw the end of European dominance of global politics and economics. The 21st century will see the end of American dominance too, as new powers, including China, India and Brazil, continue to grow and make their voices heard on the world stage. Yet the century's changes will be even deeper than a rebalancing of economics and geopolitics. The challenges of sustainable development—protecting the environment, stabilizing the world's population, narrowing the gaps of rich and poor and ending extreme poverty—will render passé the very idea of competing nation-states that scramble for markets, power and resources.

　　The defining challenge of the 21st century will be to face the reality that humanity shares a common fate on a crowded planet. We have reached the beginning of the century with 6.6 billion people living in an interconnected global economy producing an astounding $60 trillion of output each year. Human beings fill every ecological niche on the planet, from the icy tundra to the tropical rain forests to the deserts. In some locations, societies have outstripped the carrying capacity of the land, resulting in chronic hunger, environmental degradation and a large-scale exodus of desperate populations.

　　We also face a momentous choice. Continue on our current course, and the world is likely to experience growing conflicts between haves and have-nots, intensifying environmental catastrophes and downturns in living standards caused by interlocking crises of energy, water, food and violent conflict. Yet for a small annual investment of world income, undertaken cooperatively across the world, our generation can harness new technologies for clean energy, reliable food supplies, disease control and the end of extreme poverty.