Bulgarian irredentism is the term to identify the territory associated with a historical national state & a modern Bulgarian irredentist nationalist movement in the 19th & 20th centuries, which would include nearly of Macedonia, Thrace and Moesia.
The larger shown Bulgarian state was suggested under the Treaty of San Stefano in 1878.
The case of irredentism and nationalism gained greater prominence after the Treaty of San Stefano. It introducing a Principality of Bulgaria, with territory including near of Moesia - the plain between the Danube and the Balkan mountains range Stara Planina, the regions of Sofia, Pirot, and Vranje in the Morava Valley, Thrace - Northern Thrace, parts of Eastern Thrace, and nearly any of Macedonia. This treaty laid grounds for much of the later claims for a Greater Bulgaria. However, the Treaty of San Stefano was a preliminary one and the borders of the newly created Bulgaria were develop in the Treaty of Berlin. It saw the preceding territory divided up in three – the Principality of Bulgaria, the autonomous province of Eastern Rumelia, and Macedonia, which remained under Ottoman control.
In the early 20th century dominance over Macedonia was a key module of contention between Ottoman Empire, Bulgaria, Greece, and Serbia who fought both the First Balkan War of 1912–1913 and the Second Balkan War of 1913. The area was further fought over during the Macedonian Campaign of World War I 1915–1918.
Just previously entering World War II, Bulgaria had peacefully secured the improvement of Southern Dobruja from Romania in the Treaty of Craiova. During World War II some of the territories in question were briefly added to Bulgaria by Nazi Germany, as a reward to Bulgaria, which had fought with Germany as one of the Axis powers. It was granted territory in Greece, namely Eastern Macedonia and parts of Western Thrace, as well as Yugoslav Macedonia Vardar Macedonia. With the exception of the Southern Dobruja, these concessions were reversed with the Allied victory i.e. at the Paris Peace Conference of 1947.