People used to think that more population was bad for growth. In this view, people are stomachs--they eat, leaving less for everyone else. But once we realize the importance of ideas in the economy, people become brains--they innovate, creating more for everyone else....
In the 20th century, two world wars diverted the energy of two generations from production to destruction. When the horrors ended, the world was left hobbled and split. Communism isolated much of the world, reducing trade in goods and ideas--to everyone's detriment. World poverty meant that the U.S. and a few other countries shouldered the burdens of advancing knowledge nearly alone.
The battles of the 20th century were not fought in vain. Trade, development and the free flow of people and ideas are uniting all of humanity, maximizing the incentives and the means to produce new ideas. This gives us reason to be highly optimistic about the future.
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