The middle decades of the 16th century saw the revival of the spice trade routes through the Red Sea and the Gulf. It was also a time that Portugal built up its eastern empire with considerable speed, using their naval power to occupy strategic points and gain control of the Indian Ocean. Portugal was able to monopolise the stream of merchandise from Asia by blockading the entrance to the Red Sea and the Gulf and diverting supplies via the Cape of Good instead of via the Mediterranean. This strategy posed a significant threat to the interests of the Ottoman Empire and led to naval skirmishes over vital supplies – especially pepper. Eventually both empires tried to establish agreement by exchanging official letters. By the second half of the 16th century, Portugal abandoned its efforts, not having the human resources to continue naval campaigns.