One of the indirect but important causes of the age of expansion and conquest was the Crusades which started in 1095 and were completed by 1291 (there were a total of eight Crusades during this time period) as western Christendom sought to rescue both the Byzantine empire and the Holy lands from the Muslims or Turks.
The results of the Crusades were very far reaching as European soldiers brought back dramatic stories and examples of the wealth of the East in the form of perfumes, silks, spices and fruits which stimulated the demand for developing trade between the two areas.
Much of the trade as well as the crusaders themselves were transported by Italian seamen from Italian city-states. The Italian city-states and their merchants recognized the importance of the demand for Italian ships. This demand was created by the need to carry crusaders, their supplies and the new found trade between Europe and the Holy land. Consequently; the Italian city-states quickly developed a monopoly in this area.
Hence, in the political realm feudalism with its many local sovereignties gave way to the kingship which was substantially aided by these new economic forces. The kings were to impose their will on the nobles and become masters of new nations . During the fifteenth century, four national monarchies (Portugal, Spain, England , and France) consolidated their power and brought order out of the chaos created during the preceding century.