The media tends to talk about the growth of the Chinese economy as if it is something new and different. In fact, there probably have been only about 200 years in the history of civilization when China was not the largest economy on Earth. China still held this title into the early 18th century, and will get it back early in this century.
This map from the Economist (via Mark Perry) illustrates the point.
Of course there is a problem with this map. It is easy to do a center of gravity for a country, but for the whole Earth? The center in this case (unless one rightly puts it somewhere in the depths of the planet itself) depends on arbitrary decisions about where one puts the edges of the map. I presume this is from a map with North America on the far left side and Japan on the far right. If one redid the map, say, with North America in the center, Asia on the left and Europe on the right, the center of gravity would roam around North America through history.