Greek and Turkish fighter jets engaged in mock dogfights this week over the Greek island of Kastellorizo, just a mile and a half from the Turkish coast, causing tourists to flee. Meanwhile, there is a growing risk that the Turkish and Greek navies will clash, hundreds of miles to the west if Turkey pushes forward with its plans to survey for has in Greece’s exclusive economic zone. Greek officials say that all options are on the table, and German Chancellor Angela Merkel has rushed to mediate as U.S. officials remain largely absent.

There has never been any love lost between Turkey and Greece, but the danger of war between the two NATO members has not been this high since the Cyprus conflict more than forty-five years ago. In the past, Turkey and Greece have gone to the brink, but policies initiated by Turkish president Recep Tayyip Erdoğan may very much push the two neighbors over the edge.

In question are two interrelated issues: Erdoğan’s efforts to walk away from the Lausanne Treaty and his increasing desperation to find resources to bail out Turkey’s flagging economy.

The Lausanne Treaty was signed ninety-seven years ago today to tie up loose ends remaining from the collapse of the Ottoman Empire. While Kurds lament the treaty for reversing promises of statehood, the Treaty set Turkey’s borders with Bulgaria, Greece, Syria, and Iraq. Whatever flaws came with those borders, the post-Lausanne system enabled nearly a century of stability.

For reasons of ideology, economics, and ego, Erdoğan now seeks to undo the Lausanne Treaty: Ideology because Erdoğan seeks to regain control of certain Ottoman territories and change the demographics of areas outside Turkey’s borders; economics because Turkey seeks to steal resources from recognized Greek and Cypriot exclusive economic zones; and, ego, because Erdoğan wants to top Atatürk’s legacy as a military victor.

Erdoğan has already set the stage for scrapping the Lausanne Treaty. In December 2017, Erdoğan shocked a Greek audience when, on a visit to his neighbor, he floated the idea. Three months later, he suggested that the Bulgarian town of Kardzhali was within Turkey’s “spiritual boundaries,” drawing protests from Bulgaria which at the time held the European Union presidency. State-controlled Turkish newspapers have gotten in on the game showing maps of Turkey with its borders revised at the expense of neighboring states.

Read more: National Interest