On the other hand, where the hem of the continents is fertile enough to support a dense population, a large number of people are brought into contact with the sea, even where no elaborate articulation lengthens the shoreline. When this teeming humanity of a garden littoral is barred from landward expansion by desert or mountain, or by the already overcrowded population of its own hinterland, it wells over the brim of its home country, no matter how large, and overflows to other lands across the seas. The congested population of the fertile and indented coast of southern China, though not strictly speaking a sea-faring people, found an outlet for their redundant humanity and their commerce in the tropical Sunda Islands. By the sixth century their trading junks were doing an active business in the harbors of Java, Sumatra, and Malacca; they had even reached Ceylon and the Persian Gulf, and a little later were visiting the great focal market of Aden at the entrance of the Red Sea.[467] A strong infusion of Chinese blood improved the Malay stock in the Sunda Islands, and later in North Borneo and certain of the Philippines, whither their traders and emigrants turned in the fourteenth century, when they found their opportunities curtailed in the archipelago to the south by the spread of Islam.[468] Now the "yellow peril" threatens the whole circle of these islands from Luzon to Sumatra. Similarly India, first from its eastern, later from its western coast, sent a stream of traders, Buddhist priests, and colonists to the Sunda Islands, and especially to Java, as early as the fifth century of our era, whence Indian civilization, religion, and elements of the Sanskrit tongue spread to Borneo, Sumatra, Bali, Lombok, and even to some smaller islands among the Molucca group.[469] The Hindus became the dominant commercial nation of the Indian Ocean long before the great development of Arabian sea power, and later shared the trade of the East African coast with the merchants of Oman and Yemen.[470] To-day they form a considerable mercantile class in the ports of Mascat, Aden, Zanzibar, Pemba, and Natal. [Sidenote: Geographic conditions for brilliant maritime development.] On the coasts of large fertile areas like China and India, however, maritime activity comes not as an early, but as an eventual development, assumes not a dominant, but an incidental historical importance. The coastlands appearing early on the maritime stage of history, and playing a brilliant part in the drama of the sea, have been habitable, but their tillable fields have been limited either in fertility, as in New England, or in amount, as in Greece, or in both respects, as in Norway. But if blessed with advantageous location for international trade and many or even a few fairly good harbors, such coasts tend to develop wide maritime dominion and colonial expansion.[471]