When the carrack and then the caravel were developed in Iberia, European thoughts returned to the fabled East. These explorations have a number of causes. Monetarists believe the main reason the Age of Exploration began was because of a severe shortage of bullion in Europe. The European economy was dependent on gold and silver currency, but low domestic supplies had plunged much of Europe into a recession. Another factor was the centuries-long conflict between the Iberians and the Muslims to the south.