THE LEADERS of Iraq's Kurdistan region are suffering considerable consequences for their reckless staging of a referendum on independence late last month. The Iraqi government has teamed up with Turkey and Iran to impose tough sanctions, including a ban on international flights from Kurdish airports. Turkish President Recep Tayyip Erdogan, once a Kurdistan ally, is threatening to shut down an oil pipeline that provides the economically struggling region with much of its revenue. Meanwhile, the United States, long the Kurds' most important ally, has called the referendum illegitimate and done little to stanch the growing backlash.

There is a strong case for self-determination by the Kurds, a distinct nation that suffered genocide at the hands of Saddam Hussein and a long history of discrimination in Turkey, Iran and Syria. For a dozen years, post-Saddam Iraqi governments have disregarded legal obligations to Kurdistan, including the distribution of oil revenues. But Kurdistan Regional Government President Masoud Barzani has given even Kurdistan's supporters reason for opposition.

The referendum, which was opposed or only reluctantly accepted by Kurdish forces other than Mr. Barzani's Kurdistan Democratic Party, was staged largely for political reasons. Mr. Barzani, whose elected term expired four years ago, was seeking a way to revive his domestic support. In recent years he and his party have concentrated power at the expense of what was once regarded as an emerging democracy; in addition to remaining in office after his term expired, Mr. Barzani essentially shut down the parliament. Though a new legislature is supposed to be elected Nov. 1, the presidential election — and Mr. Barzani's long-promised departure from office — has been thrown into doubt by a mysterious absence of candidates.

In going forward with the referendum, Mr. Barzani disregarded the risk of undermining the alliance against the Islamic State and the potential destabilization of the moderate Iraqi government of Haider al-Abadi, who faces reelection next year. He infuriated Mr. Abadi and Mr. Erdogan by, among other things, staging the vote in areas outside the Kurdistan region, including the disputed multiethnic city of Kirkuk. He cruised through the bright red lights flashed by the Trump administration, even though Kurdistan depends heavily on the United States for its military defense.

An administration preoccupied with other foreign problems may now be tempted to let Kurdish leaders endure the results of their folly. Unfortunately, they cannot afford to do so. The United States still depends on Kurdish forces to fight the Islamic State in tandem with the Iraqi army and Shiite militias backed by Iran; the referendum has pushed those uneasy allies close to war with each other. Robust U.S. intervention is now necessary to broker truces between Kurdistan and Baghdad, as well as Ankara. The Kurds should be pressed to forswear any further steps toward independence, and to participate in next year's Iraqi elections, in exchange for the lifting of sanctions. Mr. Barzani, meanwhile, should allow his would-be country to return to democracy and the rule of law — without which it has no chance of succeeding.