A weak currency, compared to peers, helps to boost a country's export sector by making its goods more competitive than its rivals. These additional sales in turn help to boost economic growth, the jobs market, and the countries' balance of payments. A weaker currency also makes imports more expensive, pushing inflation higher.
If all else fails, the US can evoke trade sanctions against their counterparty.The Bank of Japan has actively intervened in the foreign exchange on numerous occasions since the Japanese Yen was floated against thein 1973. The central bank has intervened repeatedly over the last 25 years to either keep the currency attractive to help exporters or to try and weaken the currency to boost growth and inflation.