Convention of Constantinople (1881) in the context of Janina vilayet

Thessaly (/ˈθɛsəli/ THESS-ə-lee; Greek: Θεσσαλία, romanized: Thessalía [θesaˈli.a]; ancient Thessalian: Πετθαλία, Petthalía) is a traditional geographic and modern administrative region of Greece, comprising most of the ancient region of the same name. Before the Greek Dark Ages, Thessaly was known as Aeolia (Ancient Greek: Αἰολία, Aiolía), and appears in Homer's Odyssey.

Thessaly became part of the modern Greek state in 1881, after four and a half centuries of Ottoman rule. Since 1987 it has formed one of the country's 13 regions and is further (since the Kallikratis reform of 2011) sub-divided into five regional units and 25 municipalities. The capital of the region is Larissa. Thessaly lies in northern central Greece and borders the regions of Macedonia to the north, Epirus to the west, Central Greece to the south, and the Aegean Sea to the east. The Thessaly region also includes the Sporades islands.

The Vilayet of Janina, Yanya or Ioannina (Ottoman Turkish: ولايت يانیه, romanized: Vilâyet-i Yanya) was a first-level administrative division (vilayet) of the Ottoman Empire, established in 1867. In the late 19th century, it reportedly had an area of 18,320 square kilometres (7,070 sq mi). It was created by merging the Pashalik of Yanina and the Pashalik of Berat with the sanjaks of Janina, Berat, Ergiri, Preveze, Tırhala and Kesriye. Kesriye was later demoted to kaza and bounded to Monastir Vilayet and Tırhala was given to Greece in 1881. With the end of the Ottoman rule, the southern area of the vilayed became part of Greece and its northern area became part of Albania.

Abdülhamid II or Abdul Hamid II (Ottoman Turkish: عبد الحميد ثانی, romanized: Abd ul-Hamid-i s̱ānī; Turkish: II. Abdülhamid; 21 September 1842 – 10 February 1918) was the 34th sultan of the Ottoman Empire, from 1876 to 1909, and the last sultan to exert effective control over the fracturing state. He oversaw a period of decline with rebellions (particularly in the Balkans), and presided over an unsuccessful war with the Russian Empire (1877–78), the loss of Egypt, Cyprus, Bulgaria, Serbia, Montenegro, Tunisia, and Thessaly from Ottoman control (1877–1882), followed by a successful war against Greece in 1897, though Ottoman gains were tempered by subsequent Western European intervention.

Elevated to power in the wake of Young Ottoman coups, he promulgated the Ottoman Empire's first constitution, a sign of the progressive thinking that marked his early rule. But his enthronement came in the context of the Great Eastern Crisis, which began with the Empire's default on its loans, uprisings by Christian Balkan minorities, and a war with the Russian Empire. At the end of the crisis, Ottoman rule in the Balkans and its international prestige were severely diminished, and the Empire lost its economic sovereignty as its finances came under the control of the Great Powers through the Ottoman Public Debt Administration.