Answer:
The correct answer is: He was promoting Serbian nationalism.
Gavrilo Princip was a member of a Serbian nationalist group called the Black Hand, which aimed to create a greater Serbia by uniting Serbian-populated territories in the Balkans. The assassination of Archduke Franz Ferdinand, heir to the Austro-Hungarian Empire, was carried out in the hope that it would trigger a war between Austria-Hungary and Serbia, and ultimately lead to the unification of all Serbian territories.
Princip and his co-conspirators saw the Archduke as a symbol of Austrian oppression and hoped that his death would inspire others to rise up against their rulers. The assassination was not only an act of political violence, but also a symbolic gesture of defiance against Austria-Hungary and a statement of support for the cause of Serbian nationalism.