What was a key feature of the Treaty of Neuilly?

The Treaty of Neuilly was signed in 1919 and primarily dealt with Bulgaria following its defeat in World War I. A significant aspect of this treaty was the loss of territory that Bulgaria experienced. Under the terms of the treaty, Bulgaria ceded lands to both Yugoslavia and Romania, an action that was part of the broader redrawing of borders in Southeast Europe after the war. This loss of land significantly affected Bulgaria's economic and political landscape, contributing to national grievances and instability in the region.

The other features mentioned, such as the formation of new nations, the limitation of the army, and the setting of reparations, while relevant in the context of post-war treaties, do not specifically capture the essence of what was most impactful in the Treaty of Neuilly concerning Bulgaria. The territorial losses to neighboring countries were a defining characteristic of this treaty, making option B the correct choice.