The world’s shortest war (to date), fought in 1896, pitted England against Zanzibar, one of its Eastern African colonies. The cause of conflict was the succession to the Zanzibar sultanate. When the throne was unexpectedly vacated, a popular selection seized power, much to the chagrin of England, which preferred someone more cooperative with its policies. England brought in ships and heavy guns, shelled the palace, and secured the victory in just 45 minutes; its choice for sultan ascended the throne.
Source: Military History