Why is the US propping up the weak Japanese yen?

Over the past five years, the Japanese yen has lost 30% of its value against the US dollar and nearly as much against the pound. The currency recently hit a 40-year low against the greenback. Now, powerful figures in global finance are drawing a line in the sand.Over the weekend, Japan's Ministry of Finance and the US Treasury confirmed they had jointly intervened in currency markets to support the yen. Japan is thought to have sold $59 billion to buy yen, with Washington staging a smaller inter