It’s easy to tell summer has ended because bickering between Turkey and Greece, the Montagues and Capulets of southeastern Europe, have flared anew following a tacit truce in time for both countries' tourist season. Greek Foreign Minister Nikos Dendias last week attended the opening of the Byzantine and Christian Museum and took the opportunity to denounce Greece’s rival. “We expect Turkey to change its neo-Ottoman policy… [and] respect the monuments that other robust spiritual civilizations erected in its territory,” he said, referring to Turkey’s 2020 re-conversion of Istanbul’s iconic Hagia Sophia back into a mosque. For the Greek Orthodox Church, followed by 90 per cent of Greeks, that move was a crushing blow. The Byzantines built Hagia Sophia in 537 as the church’s patriarchal cathedral, before the conquering Ottomans converted it into a mosque in 1453, and Turkey’s founder Mustafa Kemal Ataturk made it a museum in the 1930s. An upstart major general during the Turkish War of Independence, Kemal rallied nationalist sentiment and built a fierce Turkish army from Ottoman troops scattered across Anatolia at the end of the First World War. A century ago this month, he led the Turkish battalion that clashed with, and ultimately beat back, a Greek force led by King Constantine I along the river Sakarya, outside Ankara. Turkish President Recep Tayyip Erdogan marked the centennial of the crucial Sakarya victory last week, and, to little surprise, saw fit to criticise Greece. “This episode in our history also showed us the true face of our enemy, who torched and destroyed everything in their path as they retreated from Sakarya,” he said. Mud-slinging between Turkish and Greek leaders goes back at least a millennia and a half, to the 6th century. After meeting top officials in Constantinople, Tardus, head of the Turkic Khaganate, accused the Byzantines of “speaking with ten tongues and lying with all of them”. But Sakarya helped usher in the only extended period of Turkish-Greek amity in modern times. Greece capitulated a year later, and the Treaty of Lausanne delineated the countries’ borders and a massive population exchange. Hundreds of thousands of Muslim Turks in Greece and Greek Christians in Turkey moved across the Aegean Sea – a dark coda that also marked the two as equals. In the 1930s, the neighbours agreed to trade and navigation rights, made a pact of cordial friendship and signed a mutual defence treaty with regional allies. During the Second World War, Turkey ferried food aid to Greeks facing a famine under Axis occupation. Both countries fought in the Korean War and in 1952 they were welcomed together into Nato. That same year, King Paul became the first Greek monarch to visit Turkey, and Turkish president Celal Bayar returned the favour. In 1953, Turkey, Greece and Yugoslavia signed a defence pact to deter Soviet expansion. All seemed peachy, but beneath the surface, dark forces were headed for collision. Greek Cypriots had quietly moved toward an armed struggle for union with Greece, also known as <i>enosis</i>. In 1954, Athens urged the UN to demand self-determination for Cyprus, spurring a nationalist response in Turkey, notably the creation of the “Cyprus is Turkish” association. The Turkish state had been pressurising its ethnic Greek citizens domestically for years. In 1932, the Turkish Parliament barred Turkey's Greeks — more than 100,000 had been exempted from the exchange — from dozens of top occupations, including medicine, law and carpentry. A decade later, the Turkish state levied a wealth tax on non-Muslim minorities that many saw as targeting Greek businesses. Around this time, Greece instituted a nationality code under which a non-Greek, such as one of the 100,000 Turkish Muslims in Western Thrace, who left the country with no intention of return could be deprived of citizenship. By the summer of 1955, Turkish newspapers were accusing the Ecumenical Patriarch of Constantinople of collecting donations for <i>enosis</i>, and threatening to punish Istanbul Greeks in response. After rumours spread of a Greek bomb attack on the Turkish consulate in Thessaloniki — the childhood home of Ataturk, where a Turkish staffer had in reality planted a bomb — a Turkish mob embarked on a 10-hour, overnight rampage against the Greek community of Istanbul’s Beyoglu district. Armenians and Jews were also assaulted, more than a dozen people died and hundreds of shops were destroyed by fire and rioting. The pogrom accelerated the Greek exodus from Turkey — from 70,000 in 1950 to as few as 3000 today — and turned the budding friends into bitter foes. In 1971, Turkey shuttered Istanbul’s Halki Seminary, the only place in the country where Orthodox clergymen could be educated. Three years later, the Turkish military invaded Cyprus to head off a coup, resulting in the division that stands today: an EU-member Republic of Cyprus in the south topped by the Turkish Republic of Northern Cyprus, recognised only by Ankara. A Greco-Turkish war loomed in 1987, and again in 1995, both times due to Aegean island disputes. Violations of each other’s airspace became a daily occurrence, alongside the near-constant exchange of threats and warnings. When a Greek naval vessel stopped at the Greek island of Kastellorizo off the Turkish coast in August 2020, Ankara scrambled attack helicopters, putting the two sides on the brink of war yet again. As with a long-bickering couple, when one issue pops up, a whole stew of disputes rise to the surface. Religious differences bleed into Cyprus, which touches on hydrocarbons and maritime rights, which in turn speak to territorial claims, border security and continental shelves. The issues that divide Turkey and Greece — including refugees and migration; border controls and sovereignty; international alliances and the quest for energy resources — are among the issues most crucial to the EU. Even so, the rivals have held more than 60 rounds of talks over the past two decades, yet are unable to even agree on what to discuss. Neither side is likely to back down soon, if military confidence is any indication. Turkey is preparing to launch its first domestically-produced aircraft carrier, to pair with its fleet of advanced, and accomplished, drones. Greece has moved to modernise its navy, signing major defence deals with Israel and other regional allies. And in April, the Greek air force held joint exercises with many of these same countries. Yet another opportunity arrives this week, with the UN General Assembly. Mr Dendias will be in New York and has scheduled a dozen meetings, though none with top Turkish officials. Erdogan is also expected, but his focus will be on presenting his new book, <i>A More Just World Is Possible</i>, which outlines fixes for the broken international system. Expect the squabbling to continue for the foreseeable future. At least until the next game-changing episode, Athens and Ankara are going to keep giving each other the side-eye.