Ferdinand Verbiest, Antoine Thomas and the idea of spreading Christianity into Tartary

Since the Mongol invasion of northern Europe in 1241, European people became aware that the Central Asian grasslands were inhabited by terrifying horsemen tribes. At first, Franciscan friars were sent in “mission” to the court of Mongol Khans in order to obtain military information and try to establish diplomatic relations. During the seventeenth century the Tartars were no longer a threat for Europe and the overland route to Tartary/China was impassable, as a result the Jesuits and missionaries of other orders reached China through the sea route on Portuguese ships. When the first Jesuits arrived in China they had a poor knowledge of Tartary based mainly on second-hand reports and accounts, nevertheless the idea of spreading the Gospel beyond the Great Wall was already in their minds. Martino Martini was among the first one to suggest Tartary as a new land for evangelization. However, it was not until Verbiest's first journey in Tartary in 1682 that the idea of spreading Christianity among the Tartars was seriously taken into account. Antoine Thomas, Verbiest's countryman and secretary, was the main supporter of this idea. In several letters Thomas expressed the desire that the Christian Faith could reach the grassland, according to his correspondence, the main points for achieving this goal were: the study of the language; the translation of Christian texts into Manchu and Mongolian languages; the building of churches into the steppe; the defeat of the Zunghar leader Galdan. Thomas was also active in the map-making of Tartary and a supporter of the overland route to Europe. Why this “plan” was never put in practice? Which were the problems and difficulties in carrying on such task?