After yearning for independence for generations, Kurds in Iraq are scheduled to take a major step in that direction with a nonbinding referendum set for Sept. 25. The vote, expected to endorse a separate state, would be a mistake, increasing turmoil in a part of the world roiled by the fight against the Islamic State and further threatening Iraq’s territorial integrity. Postponement makes better sense.

In many ways, independence is a logical next step for the five million Iraqi Kurds, who carved out their semiautonomous enclave after the 1991 gulf war. Now that their military forces have played a pivotal role in helping to defeat the Islamic State, the Kurds think they are entitled to this long-promised referendum.

Kurdistan has evolved into a relatively peaceful region. It was lucky enough to have oil and gas resources that opened up trade with Turkey and Iran and brought needed revenue. After the 2003 American invasion, Washington worked with the Iraqis to draw up a constitution that ensured Kurdistan’s semiautonomous status.

There are also serious problems. Two families, the Barzanis and the Talabanis, control politics; corruption is widespread. Because of political infighting, Kurdistan’s parliament has not met since October 2015; the region’s president, Masoud Barzani, remains in office four years after his term ended. Declining oil prices and disputes with Iraq’s central government have left the Kurdistan government in debt. Kurdish authorities are accused of discriminating against minorities. Could Kurdistan make it as an independent state if Iraq and neighboring states stayed hostile to the idea?

The Kurds have sought an independent state since at least the end of World War I. While the Constitution guarantees them a role in the federal government as well as regional autonomy, the Kurds don’t believe the Shiite majority has given them a fair shake. But the referendum would heighten tensions, make it harder to stabilize Iraq and divert attention as the United States, Iraq and their partners work to defeat ISIS and rebuild Iraqi communities.

Some Kurds have dreamed of merging the whole community — 30 million people across Turkey, Iraq, Syria and Iran — into a single entity. That’s not feasible now and worries leaders in Turkey and Iran who see a greater Kurdistan as a territorial threat. Turkey’s deputy prime minister recently warned that the Iraq vote would “contribute to instability.” Iraq’s prime minister said the vote would be “illegal” because it conflicts with Kurdistan’s constitutional commitments as part of Iraq’s federal government. One sore point is that the boundaries in the referendum include Kirkuk, an oil-rich area the Kurds control and want to incorporate.

The Americans and Europeans have urged the Kurds to postpone the vote until after next year’s Iraqi elections. Mr. Barzani responded by assuring critics the vote would not lead immediately to independence but rather a prolonged negotiation with Baghdad over a split. At this point, postponement is the better option. A Kurdish breakaway is risky; without sufficient preparation, it would further marginalize Iraq’s Sunni minority, already disenfranchised by the Shiite majority and prey to Sunni extremists like ISIS.

On Sunday, a Kurdish official told Reuters the Kurds may delay the vote in return for concessions from Baghdad.

Self-determination is an understandable goal. But just voting for independence is no guarantee that whatever state emerges will govern fairly or well. It does the Kurdish people little good if their leaders do not make a strong effort to first ensure that Kurdistan’s democratic institutions are functioning, the economy is strong and they have support from Iraq and other countries before striking out alone.