why the U.S. stepped in

Manuel Augusto Moreno | Moment | Getty Images Washington’s decision to join Japan in supporting the battered yen has prompted questions over what motivated the rare coordinated intervention, with analysts pointing to concerns over U.S. Treasury markets and Japan’s financial system. Tokyo has grown increasingly wary of the yen’s decline, which recently dropped to its weakest level against the dollar in nearly four decades. The yen had been hovering at multi-decade lows, sliding to 163.73 per dollar last Thursday before rebounding to 157.57 Friday. The coordinated intervention was the first U.S.-Japan joint operation to buy yen since 1998, and the…