The price of bitcoin has dropped to an 18-month low as instability in cryptocurrency markets, driven by a dispute over the future of Bitcoin Cash, prompted mass selloffs across the board.

Bitcoin Cash is both a rival cryptocurrency to bitcoin and a fork or splitoff of cryptocurrency that launched in August 2017. The fourth-largest cryptocurrency by market capitalization today, Bitcoin Cash found a willing audience given that everyone who held bitcoin at the time of the fork were credited with the same amount in Bitcoin Cash.

The dispute over the future of Bitcoin Cash appears from the outside to be like teenage girls fighting in a schoolyard. In one corner, Roger Ver, aka “Bitcoin Jesus,” and his supporters are arguing for a tweak to the Bitcoin Cash protocol to create what is now dubbed “Bitcoin ABC.” In the other corner, Craig Wright, the Australian who once claimed he was bitcoin founder Satoshi Nakamoto, argues that the protocol should be maintained close to what it is now.

Wright is expected to win the battle for control of Bitcoin Cash, but the result will likely see a significant number of Bitcoin Cash proponents, led by Ver, supporting a forked version of the cryptocurrency, Bitcoin ABC.

As Ars Technica noted, “the controversy is internal to Bitcoin Cash … so it’s not clear why it should have any negative impact on the value of mainstream bitcoin or other cryptocurrencies. But cryptocurrency trading tends to be highly correlated — when one cryptocurrency starts to fall in value, others often follow.”

Not surprising given it’s the source of the contagion, the price of Bitcoin Cash has plummeted, losing more than 30 percent of its value in the last seven days. It’s down nearly 18 percent today, to $428.63. At its peak during the cryptocurrency frenzy of late 2017, Bitcoin Cash hit $4,091.70, meaning it has now lost about 90 percent of its value in nearly 12 months.

The selloff was across the board. All major cryptocurrencies, including Ethereum, Litecoin and Ripple XRP, saw drops of between 10 and 20 percent.

As of 9:40 p.m. EST, bitcoin was trading at $5,510.23, down almost 12 percent according to figures from Coindesk — its lowest level since May 2017.