Because of the abundance and quality of New World furs, around the middle of the 16th century they became the prime reason for trans-Atlantic journeys. Beginning in the 1620s European demand for furs became insatiable, with beaver pelts being particularly sought after. It was thanks to the knowledge of the Indigenous people and their understanding of fur-bearing animals that the coureurs de bois were able to build a commercial venture of worldwide importance, the development of which forms a dominant theme in early Canadian history. The fur trade was the object of so much competition and rivalry that it led to a monopoly system that provided the financial base for subsequent exploration and settlement.