About one month after Japan and the US joined forces to prop up the yen, strategists say the intervention succeeded in slowing the currency's short-term slide but did little to alter the forces driving its longer-term decline. After the coordinated intervention, the yen climbed from a four-decade low of around 164 per dollar to 155.23. But that boost proved unsustainable, with the currency already approaching 160 against the dollar again.