Pirin Macedonia in the context of "Kingdom of Yugoslavia"

Under the reign of Philip II (359–336 BC), the ancient kingdom of Macedonia, initially at the periphery of classical Greek affairs, came to dominate Ancient Greece in the span of less than 25 years, largely thanks to the character and policies of its king. In addition to utilising effective diplomacy and marriage alliances to achieve his political aims, Philip II was responsible for reforming the ancient Macedonian army into an effective fighting force. The Macedonian phalanx became the hallmark of the Macedonian army during his reign and the subsequent Hellenistic period. His army and engineers also made extensive use of siege engines. Chief among Philip's Thracian enemies was the ruler Kersebleptes, who may have coordinated a temporary alliance with Athens. In a series of campaigns stretching from 356 to 340 BC, Philip II managed to ultimately subjugate Kersebleptes as a tributary vassal, conquering much of Thrace in the process. Philip II also fought against the Illyrian king Bardylis, who threatened Macedonia proper, and against Grabos II and Pleuratus in Illyria (centred in modern-day Albania). In his newly conquered territories, he founded new cities such as Philippi, Philippopolis (modern Plovdiv, Bulgaria), Herakleia Sintike (Pirin Macedonia, Bulgaria), and Herakleia Lynkestis (modern Bitola, North Macedonia).

Philip II eventually campaigned against the city-state of Athens and her allies in the Aegean region, as well as Thebes after the decline of its hegemony in mainland Greece. In the defence of the Amphictyonic League of Delphi and in conjunction with the Thessalian League, Macedonia became a key player in the Third Sacred War (356–346 BC), defeating the Phocians, commanded by Onomarchus, at the Battle of Crocus Field in 352 BC. While poised to launch a direct assault on Athens in 346 BC, the Macedonian king was met with an Athenian embassy that arranged the Peace of Philocrates. As a result, Macedonia and Athens became allies, yet Athens was forced to relinquish its claims to the city of Amphipolis (in modern-day Central Macedonia).

Vardar Macedonia (Macedonian and Serbian: Вардарска Македонија, romanized: Vardarska Makedonija) is a historical term referring to the northern part of the broader Macedonian region, roughly corresponding to present-day North Macedonia. The name derives from the Vardar River and is primarily associated with the period of Serbian (1912–1918) and later Yugoslav rule (1918–1991).

Macedonians (Bulgarian: македонци), or Macedonian Bulgarians (Bulgarian: македонски българи), sometimes also referred to as Macedono-Bulgarians, Macedo-Bulgarians, or Bulgaro-Macedonians, are a regional, ethnographic group of ethnic Bulgarians, inhabiting or originating from the region of Macedonia. This is how the majority of Slavic-speaking population of Macedonia had been referred to by most of the national conscious minority among them and by outside observers, from the 10th until the early 20th century in a sense of a demonym at first, and later as an social class synonym mainly, and as ethnonym. Since 1913, the Macedonian Bulgarian population is largely concentrated in Pirin Macedonia but much is spread across the whole of Bulgaria and the diaspora.