In 1938, the Republic of Hatay became independent from the French mandate of Syria as the Republic of Hatay and following a referendum, 8 months later in 1939, it decided to join Turkey. This self-annexation was never recognized by Syria, which continues to show the Hatay Province of Turkey as part of Syria's territory on maps.
At present, Syrians hold the view that this land is historically Syrian and was illegally ceded in the late 1930s to Turkey by France – the mandatory occupying power of Syria (between 1920 and 1946). The Turks remember Syria as a former Ottoman vilayet. In 1938, the Turkish Army went into the former Syrian Mediterranean province with French approval and expelled most of its Alawite Arab and Armenian inhabitants. Before this, Alawi Arabs and Armenians were the majority of the provincial population. For the referendum, Turkey crossed tens of thousands of Turks into Alexandretta to vote.
In 1938, the province declared its independence from France and the following 29 June, the parliament of the newly declared Hatay Republic voted to join Turkey. This referendum has been labeled both "phoney" and "rigged", and that it was a way for the French to let Turks take over the area, hoping that they would turn on Hitler. The Syrian government recognized this decision in 2004 and gave up on territorial claims. Syrians still consider this land as integral Syrian territory. Syrians call this land Liwaaa aliskenderuna rather than the Turkish name of Hatay.
...documents demonstrate that there is a “missing dimension” in the established historiography of the Middle East in those years. They cover the period between October 1945 and December 1946 and address Turkish-Syrian relations against the backdrop of the inter-Arab and Anglo-Soviet rivalry over the future of Syria in the early years of the Cold War. Then, as today, the weakness and lack of stability of the Syrian state prompted Turkey to intervene in Syria in an attempt to replace the anti-Turkish republican regime headed by President Shukri al-Quwatli (Doc. 8) with a friendly Hashemite monarchy under King Abdallah, which was to include Syria and Lebanon in addition to Transjordan and was to be linked with the Hashemite kingdom in Iraq. (Docs. 12, 13)
The borders between Turkey and Syria are not, as far as we know, an issue today, but after World War II the two countries were engaged in a territorial dispute. Their quarrel over the province of Alexandretta became a source of tension in Turkish-Syrian relations, and also played a part in the Anglo-Soviet secret war in the Middle East. The province of Alexandretta (Hatay), with its strategic port city of the same name, had been part of Syria under the French mandate in 1920-1936. Turkey claimed the province, arguing that its Turkish inhabitants comprised the majority. On the eve of World War II, France, seeking Turkey’s cooperation against Nazi Germany, tacitly agreed to relinquish the province, despite strong protests from the Syrian leaders. In June 1939, Turkey took over the province, causing thousands of Arab and Armenian refugees to flee to Syria. After the war, the Syrian nationalist leaders sought to exploit Britain’s designs to incorporate their country in a regional defense alliance with Turkey and Iraq against the Soviet Union, to demand the return of the province.
...secret Turkish-Hashemite negotiations in November-December 1946 reveal that, apart from Alexandretta, Turkey harbored territorial designs over Aleppo and Kamishli, the main Kurdish city in north-eastern Syria. (Doc. 14)...
...Britain was involved not only in the efforts to solve the problem of Alexandretta, but took part behind the scenes in the negotiations on the secret agreement of December 1946 between the Turkish, Iraqi and Jordanian leaders to form a Hashemite Greater Syrian monarchy. (Docs. 11,) This was part of a more elaborate plan devised by British intelligence agents with the tacit agreement of Foreign Secretary Ernest Bevin. Its first step was implemented in November and December 1946 and entailed the removal of the anti-Hashemite and anti-Turkish Syrian prime minister, Sa’adallah al-Jabiri, and his replacement with Jamil Mardam, who was secretly collaborating with the British agents and Nuri al-Said. Its more ambitious goal was to solve the conflict between the Hashemite and Saudi royal families by forming two large monarchies – one under the Hashemites in the Fertile Crescent in the north, and a Saudi monarchy that would extend over most of the Arabian Peninsula in the south, including Yemen. Bevin informally proposed such a plan to Prince Faisal, Ibn Saud’s son, in January 1947, but the Saudi king turned it down...
... On the one hand there is Arab aversion to the “return of the Ottoman Empire” to the Arab world, and on the other, readiness in certain instances to seek Turkish intervention. In this regard, the present Islamist prime minister, Recep Tayyip Erdogan is in a better position to intervene in the Arab world than was President Inonu, who represented the nationalist secularist Kemalist Turkish Republic.
Will that be an "illegal occupation"?