Let’s see . . .
Greece come up with the Megali Idea, a goal of reuniting all the provinces that were once part of the Byzantine Empire, and negotiates a deal for most of them to be Greece’s part of spoils when the Ottoman Empire is partitioned, in return for joining the Allies in WWI. Greece then gets stabbed in the back by Britain and France who grab the majority of the area Greece claims, including Constantinople/Istanbul for themselves. They do however give the Greeks Thrace (East and West) and Ionia/Smyrna. This took place in August 1920..
Not quite. Nobody ever promised Greece most of the provinces that were once part of the Byzantine Empire. All of Turkey, & a lot more, was once Byzantine.
France didn't occupy any land promised to Greece, though some of what it occupied was claimed by Greece, & part of it was occupied by Greece in 1920 (the French withdrew: they were heavily outnumbered). It occupied SE Turkey, & small parts of NW Anatolia alongside the British, e.g. Bursa (the first Ottoman capital - the tombs of the first sultans are there). Britain occupied Istanbul & both sides of the straits, but it was always meant to be a temporary occupation, & had never promised any of that to Greece. The Greeks had demanded it (plus a lot more, including southern Albania, half of Bulgaria, most of the Turkish coast & all of western Anatolia - a territory which would have had a large non-Greek majority), & been refused.
Izmir was to be occupied & administered by Greece, but not formally ceded. Its future was left ambiguous.
So Greece decides to go for the rest of Anatolia in compensation, using the claim that they are protecting the majority ethnic Greek population, which was about as accurate as the Sunni claim that they were the majority of the population of Iraq before OIF. The Greeks advanced was generally successful for nearly a year, then stalemated for 8 months. The Turks then attacked in late August 1922, and drove the Greek Army out of Ionia falling in a 2 week offense. The Turks then turned north toward Istanbul, but the British, French, and the Italians were unwilling to face them in combat and withdrew. East Thrace was returned to the Turks as part of the peace treaty between the Ottoman Empire, Britain, France, and Italy the following month.
Not as compensation, but just from a kind of collective insanity. It was the Megali Idea. They were trying to grab the lands they'd asked for, & been refused, at the peace conference. The Armenians had a similar fit of lunacy, demanding all of eastern Turkey, most of the Mediterranean coast, half of Georgia, half of Azerbaijan & a slice of NW Iran: a territory from the Med to the Caspian, in which Armenians would have been outnumbered by each of four or five other peoples. It overlapped with the Greek demands.
The French fought in the SE, but lost. They might have been able to win if they'd tried harder, but there was deep reluctance to commit more strength. They had small garrisons, many of them largely Armenian, which were isolated & attacked by Turks & Kurds until they withdrew, one by one. Like the British, they weren't attacked in the NW & withdrew without fighting.
The Italians were only in the SW, never established much of a presence, & decided not to stay when it became apparent they'd have to fight hard to hold on.
So East Thrace and Ionia were Greek territory for less than 3 years, and the majority of the population of both was Turkish before war.
Correct. There were towns & districts with a Greek majority, but neither region had a Greek majority, even allowing for understatement of minorities in the last Ottoman census. Nor did West Thrace, IIRC: more Turks & Bulgarians (another population exchange) left than Greeks remained.