The Northern Crusades or Baltic Crusades were Christian colonization and Christianization campaigns undertaken by Catholic Christian military orders and kingdoms, primarily against the pagan Baltic, Finnic and West Slavic peoples around the southern and eastern shores of the Baltic Sea, and to a lesser extent also against Orthodox Christian Slavs.
The most notable campaigns were the Livonian and Prussian crusades. Some of these wars were called crusades during the Middle Ages, but others, including most of the Swedish ones, were first dubbed crusades by 19th-century romantic nationalist historians. However, crusades against Estonians, but also against 'other pagans in those parts' were authorized by Pope Alexander III in the bull Non parum animus noster, in 1171 or 1172.