system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why did Gavrilo Princip assassinate Francis Ferdinand and what exactly was the Black Hand?
gpt
The Black Hand was a secret society based out of Serbia comprised of a number of members of the Serbian military. Their main purpose was the reunification of southern slavic territories under Serbian rule.

Now a major portion of ethnic Slavs lived in territory controlled by the Austro-Hungarian Empire, and like many ethnic minorities in a large empire, the slavs weren't treated too well.

Franz Ferdinand was the crown prince of the Austro-Hungarian Empire, thus a figurehead and symbol of the oppression of the slavic people in the Empire. As such, he was a prime target for assassination for people who wanted independence/reunification of Serbian people.

Gavrilo Princip was one such person, belonging to a nationalist group called 'Young Bosnia' (Bosnia being of the territories in the Empire that was mostly ethnic Slavs). The actual assassination of Franz involved a number of people but Princip was the one who succeeded.

Ironically, the Austrian Army Chief of Staff had been petitioning the Emperor to go to war with Serbia for years, but had been opposed on every occasion by none other than Franz Ferdinand. In fact, Franz was in favour of granting more autonomy for the ethnic minorities in the Empire. Arguably, Gavrilo shot the one man in the Empire who could've helped his group's cause the most.