in Tibet proper, until this practice was prohibited after China took over Tibet in 1950–51. The nomadic Sami people, an indigenous people of northern Finland, Sweden, Norway, and the Kola Peninsula of Russia, practise a form of nomadic transhumance based on reindeer. In the 14th and 15th century, when reindeer population was sufficiently reduced that Sami could not subsist on hunting alone, some Sami, organized along family lines, became reindeer herders. Each family has traditional territories on which they herd, arriving at roughly the same time each season. Only a small fraction of Sami have subsisted on reindeer herding over the past century; as the most colorful part of the population, they are well known. But as elsewhere in Europe, transhumance is dying out. The Mesta was an association of sheep owners, (Spanish nobility and religious orders) that had an important economic and political role in medieval Castile. To preserve the rights of way of its transhumant herds through cañadas, the Mesta acted against small peasants. In Chad, nomadic pastoralists include the Zaghawa, Kreda, and Mimi. Farther north in Egypt and western Libya, the Bedouins also practice pastoralism. Cross-border pastoralism Sometimes nomadic pastoralists move their herds across international borders in search of new grazing terrain or for trade. This cross-border activity can occasionally lead to tensions with national governments as this activity is often informal and beyond their control and regulation. In East Africa, for example, over 95% of cross-border trade is through unofficial channels and the unofficial trade of live cattle, camels, sheep and goats from Ethiopia sold to Somalia, Kenya and Djibouti generates an estimated total value of between US$250 and US$300 million annually (100 times more than the official figure). This trade helps lower food prices, increase food security, relieve border tensions and promote regional integration. However, there are also risks as the unregulated and undocumented nature of this trade runs risks, such as allowing disease to spread more easily across national borders. Furthermore, governments are unhappy with lost tax revenue and foreign exchange revenues. There have been initiatives seeking to promote cross-border trade and also document it, in order to both stimulate regional growth and food security, but also to allow the effective vaccination of livestock. Initiatives include Regional Resilience Enhancement Against Drought (RREAD), the Enhanced Livelihoods in Mandera Triangle/Enhanced Livelihoods in Southern Ethiopia (ELMT/ELSE) as part of the Regional Enhanced Livelihoods in Pastoral Areas (RELPA)