Potato blight triggers a famine that kills about a million people and drives more than a million to emigrate from Ireland.
A series of armed conflicts between the colonial government and Māori iwi, chiefly over land and sovereignty, which led to large confiscations of Māori land.
The Qing cede Hong Kong Island to Britain and open five treaty ports, the first of China's unequal treaties.
A wave of revolutions sweeps Europe, from France to the German states, Austria, Italy and Hungary, demanding democratic reform and national self-determination.
Karl Marx and Friedrich Engels publish in London a pamphlet setting out the theory of class struggle, one of the most influential political texts ever written.
Representatives of the British Crown and many Māori chiefs signed the Treaty of Waitangi, New Zealand's founding document; differences between its English and Māori texts remain debated.
Louis Daguerre's photographic process is made public in France, the first commercially successful form of photography.