As recently as 1990, the United States accounted for a quarter of the world economy. The European Union was just a little over a quarter. Japan, east Asia and India combined made up roughly another quarter; Japan on its own was about a tenth of global GDP. (Australia was then, and still is, just over 1 per cent of global GDP.)
In 2010, the US share was about 20 per cent of world GDP, about the same as the European Union. By then, Asia was making up just under a third of the total.