Yet despite so promising a start, the process of Turkey’s accession to the E.U. has lost significant momentum since 2005. Negative statements and actions by E.U. leaders have played a key role in discouraging Turkey. These have undermined Ankara’s will to reform and have fueled resentment. Popular support in Turkey for E.U. membership continues to wane. Frustrated leaders in Turkey lament that the E.U. would reject Turkey’s accession even if Ankara implements all the prerequisite reforms and meets all other preconditions.

Europe’s wavering on Turkey’s E.U. accession is jeopardizing the E.U.’s credibility and threatening to tarnish its good image. How can European leaders be trusted if they continue to go back on their word, stalling, and perhaps scuttling, a process that began a decade ago with so much promise, has produced so many positive effects, and holds such potential for the future?

During my three decades in mediating conflicts around the globe, I have learned that only rarely, perhaps once in a generation, do the political planets align for dramatic solutions. (In the past few years just such an alignment appeared over Northern Ireland.)

A promising alignment is now appearing over a land of key importance for both the E.U. and Turkey: Cyprus. Ongoing talks between the leaders of the island’s Greek and Turkish communities offer the best and probably the last chance to avoid an indefinite partition of the island. A settlement on Cyprus — something that both Turkey and the E.U. can contribute to achieving — would breathe new life into the accession negotiations between Turkey and the E.U. and hasten the day when both sides can gain full advantage from each other.

Strengthening the relationship between Turkey and the E.U. through accession negotiations offers a clear opportunity to serve the E.U.’s interests in energy security and to bolster stability both in the Middle East and the South Caucasus.