Vassal state in the context of "Protectorate of the Western Regions"

Rumelia (Ottoman Turkish: روم ايلى, romanized: Rum İli, lit. 'Land of the Romans'; Turkish: Rumeli; Greek: Ρωμυλία) was a historical region in Southeastern Europe that was administered by the Ottoman Empire, roughly corresponding to the Balkans. In its wider sense, it was used to refer to all Ottoman possessions and vassals in Europe. These would later be geopolitically classified as "the Balkans", although Hungary and Moldova are sometimes excluded. In contemporary English sources, Rumelia was known as Turkey in Europe.

The Balkan campaign of Alexander the Great took place in 335 BC, against a number of rebellious vassals of the Macedonian kingdom. Alexander successfully pacified each in turn, leaving him free to begin the long-planned invasion of Persia.

In 336 BC, while attending the wedding of his daughter by Olympias, Cleopatra and Olympias' brother, Alexander I of Epirus at Aegae, Philip II was assassinated by the captain of his bodyguard, Pausanias. Philip's son, and previously designated heir, Alexander was proclaimed king by the Macedonian noblemen and army.

The kingdom of Macedonia was an ancient state in what is now the Macedonian region of northern Greece, founded in the mid-7th century BC during the period of Archaic Greece and lasting until the mid-2nd century BC. Led first by the Argead dynasty of kings, Macedonia became a vassal state of the Achaemenid Empire of ancient Persia during the reigns of Amyntas I of Macedon (r. 547 – 498 BC) and his son Alexander I of Macedon (r. 498 – 454 BC). The period of Achaemenid Macedonia came to an end in roughly 479 BC with the ultimate Greek victory against the second Persian invasion of Greece led by Xerxes I and the withdrawal of Persian forces from the European mainland.

During the age of Classical Greece, Perdiccas II of Macedon (r. 454 – 413 BC) became directly involved in the Peloponnesian War (431–404 BC) between Classical Athens and Sparta, shifting his alliance from one city-state to another while attempting to retain Macedonian control over the Chalcidice peninsula. His reign was also marked by conflict and temporary alliances with the Thracian ruler Sitalces of the Odrysian Kingdom. He eventually made peace with Athens, thus forming an alliance between the two that carried over into the reign of Archelaus I of Macedon (r. 413 – 399 BC). His reign brought peace, stability, and financial security to the Macedonian realm, yet his little-understood assassination (perhaps by a royal page) left the kingdom in peril and conflict. The turbulent reign of Amyntas III of Macedon (r. 393 – 370 BC) witnessed devastating invasions by both the Illyrian ruler Bardylis of the Dardani and the Chalcidian city-state of Olynthos, both of which were defeated with the aid of foreign powers, the city-states of Thessaly and Sparta, respectively. Alexander II (r. 370 – 368 BC) invaded Thessaly but failed to hold Larissa, which was captured by Pelopidas of Thebes, who made peace with Macedonia on condition that they surrender noble hostages, including the future king Philip II of Macedon (r. 359 – 336 BC).

A suzerain (/ˈsuːzərən, -reɪn/, from Old French sus "above" + soverain "supreme, chief") is a person, state or polity who has supremacy and dominant influence over the foreign policy and economic relations of another subordinate party or polity, but allows internal autonomy to that subordinate. Where the subordinate polity is called a vassal, vassal state or tributary state, the dominant party is called the suzerain. The rights and obligations of a vassal are called vassalage, and the rights and obligations of a suzerain are called suzerainty.

Suzerainty differs from sovereignty in that the dominant power does not exercise centralized governance over the vassals, allowing tributary states to be technically self-ruling but enjoy only limited independence. Although the situation has existed in a number of historical empires, it is considered difficult to reconcile with 20th- or 21st-century concepts of international law, in which sovereignty is a binary concept, which either exists or does not. While a sovereign state can agree by treaty to become a protectorate of a stronger power, modern international law does not recognise any way of making this relationship compulsory on the weaker power. Suzerainty is a practical, de facto situation, rather than a legal, de jure one.

The Principality of Bulgaria (Bulgarian: Княжество България, romanized: Knyazhestvo Balgariya) was a vassal state under the suzerainty of the Ottoman Empire. It was established by the Treaty of Berlin in 1878.

After the Russo-Turkish War ended with a Russian victory, the Treaty of San Stefano was signed by Russia and the Ottoman Empire on 3 March 1878. Under this, a large Bulgarian vassal state was agreed to, which was significantly larger: its lands encompassed nearly all ethnic Bulgarians in the Balkans, and included most of Moesia, Thrace and Macedonia, stretching from the Black Sea to the Aegean. However, the United Kingdom and Austria-Hungary were against the establishment of such a large Russian client state in the Balkans, fearing it would shift the balance of power in the Mediterranean. Due to this, the great powers convened and signed the Treaty of Berlin, superseding the Treaty of San Stefano, which never went into effect. This created a much smaller principality, alongside an autonomous Eastern Rumelia within the Ottoman Empire.

The Battle of Köse Dağ took place in eastern Anatolia on 26 June 1243 when an army of the Sultanate of Rum, led by Sultan Kaykhusraw II, confronted an invading Mongol army under the general Baiju and was decisively defeated. The battle was the pivotal event of the Mongol conquest of Anatolia: Rum, previously a significant independent power in the eastern Mediterranean, was reduced to the status of a client kingdom, and its territories were later absorbed into the Mongol Ilkhanate.

The Mongol Empire first achieved territorial contact with Rum in the early 1230s by conquering a large swathe of western Iran, but largely left it alone over the next decade. Instead, under their general Chormaqan, Mongol armies subjugated Transcaucasia and reduced the Kingdom of Georgia to a vassal state. Relations deteriorated after the accession of Kaykhusraw II to the Rum throne in 1237, and Mongol raids on Rum territory began in 1240. Two years later, Baiju, who had replaced Chormaqan after the latter became disabled, captured and pillaged the city of Erzurum, escalating hostilities into open war. He again invaded Rum in 1243, with an army of 30,000 Mongol troops accompanied by Georgian and Armenian auxiliaries.

A client state, in the context of international relations, is an umbrella term that broadly refers to any state economically, politically, and militarily subordinated to a more powerful controlling state. It typically describes a bilateral relationship that is mutually beneficial, characterized by different but shared obligations.

Variants of a client state are associated state, dominion, condominium, self-governing colony, neo-colony, protectorate, puppet state, satellite state, vassal state and tributary state.

The Ottoman Empire had a number of tributary and vassal states throughout its history. Its tributary states would regularly send tribute to the Ottoman Empire, which was understood by both states as also being a token of submission. In exchange for certain privileges, its vassal states were obligated to render support to the Ottoman Empire when called upon to do so. Some of its vassal states were also tributary states.

These client states, many of which could be described by modern terms such as satellite states or puppet states, were usually on the periphery of the Ottoman Empire under suzerainty of the Sublime Porte, over which direct control was not established. The Ottoman Empire maintained relationships with various states, some of which were under their direct rule (provinces) and others that were vassal states or tributary states, meaning they recognized Ottoman suzerainty but retained a degree of autonomy.