The yen has tumbled past a 40-year low against the U.S. dollar, prompting the Japanese government to vow “appropriate action at any time.”

The currency has been falling for years and broke through ¥162 against the dollar on Tuesday, the weakest since 1986, compared to a high of around ¥75 in 2011.

Here’s a look at the causes and consequences and how Japan might halt the slide, which mirrors drops in other Asian currencies in the wake of the Middle East war.