This BBC report on Japan, save for the first few paragraphs, focuses on the fertlity problem. Japan is the worlds least fertile nation. The Japanese have a word for it, "shoshika," meaning a society without children. "By 2007, Japans population is expected to peak at 127 million, then shrink to under 100 million by the middle of the century. This means 30 million fewer workers at a time when the number of elderly will have almost doubled." This decline of the population by about 20% will have consequences, inlcuding the possibility of slipping into a permanent recession. Allowing foreigners in from, say, the Phillipines, is an option, but not something that Japanese readily take to.
In contrast to Japan - and of course the European Union - the US population is expected to increase by 46% to 420 million by the middle of the century. Also note HREF="http://news.bbc.co.uk/1/hi/world/asia-pacific/3708098.stm">this, and the useful graph at the bottom of the article.