Why the U.S. stepped in after decades to prop up Japan's yen — and what's at stake

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.