They’re back. Or perhaps they never went away.

Currency wars are making headlines again with the Bank of Japan’s decision to double its inflation target to 2% while committing to open-ended asset purchases next year. The news comes as Japanese Prime Minister Shinzo Abe has been pressuring the central bank to devalue the yen.

Bloomberg reports this move is the BOJ's strongest commitment yet to end two decades of stagnation. The yen rose after the announcement, signaling that some investors were disappointed with the BOJ's decision.

Related: “The Yen Is Doomed”: For Japan, This Time Really Is Different, Merk Says

Bundesbank head Jens Weidmann is the latest policymaker to warn of a brewing currency war, according to Reuters. He joins Russian Central Banker Alexei Ulyakeyev and St. Louis Fed President James Bullard, who have both accused Tokyo of monetary protectionism and raising the specter of “beggar thy neighbor" policies.

U.S. automakers have even weighed in on Japan's monetary policies. Detroit News reports a trade group representing the Big Three opposes the BOJ's efforts and has urged Obama to denounce them, arguing that Japan is trying to restrict access to the auto market there.

Jim Rickards, author of Currency Wars and senior managing director at New York-based investment bank Tangent Capital Partners, says a currency war between Japan and the U.S. started years ago.

“It’s really a continuation of the currency war that began in 2010 started by the Fed and Treasury to devalue the dollar,” Rickards tells The Daily Ticker.

Referencing the currency wars of the 1920s and 1930s, Rickards says these fights go on for 5 to 15 years, and he expects competitive devaluations to continue.

“They keep going on, that’s what 'beggar thy neighbor' is all about,” he argues. “The U.S. started devaluation in 2010, but then you have Brazil, Switzerland, now Japan and others joining in. It’s like a ping-pong match. It goes back and forth.”

It’s a game of ping-pong that nobody wins. Rickards says currency wars can lead to inflation or trade wars and sometimes even actual wars.

Rickards cites Singapore and Europe as two examples of regions that aren’t cheapening their currency to promote exports. This is just one reason why Rickards has been bullish on these currencies.

“When you have two currencies, they can’t both devalue against each other at the same time, it’s mathematically impossible,” he says. “So if you understand the U.S. wants a cheaper dollar, you have to have a stronger euro. There’s no other way it can play out.”

Earlier this month, the euro hit a nine-month high against the dollar.