Final answer:
The Black Hand assassinated Franz Ferdinand as part of their goal to create Greater Serbia by separating Bosnia-Herzegovina from Austria-Hungary. Gavrilo Princip, a member of the Black Hand, carried out the assassination when the opportunity presented itself.
Step-by-step explanation:
The Black Hand assassinated Franz Ferdinand because they wanted to separate Bosnia-Herzegovina from Austria-Hungary and annex it to form 'Greater Serbia'. The group, which consisted of Serbian officers, trained a group of college students to carry out the assassination. One of those students, Gavrilo Princip, seized an opportunity when the Archduke became lost and stuck in traffic, and shot him and his wife.