The Indian Ocean trade routes connected Southeast Asia, India, Arabia, and East Africa. From at least the third century BCE, long distance sea trade moved across a web of routes linking all of those areas as well as East Asia (particularly China). Long before Europeans "discovered" the Indian Ocean, traders from Arabia, Gujarat, and other coastal areas used triangle-sailed dhows to harness the seasonal monsoon winds. Domestication of the camel helped bring coastal trade goods - silk, porcelain, spices, slaves, incense, and ivory - to inland empires, as well.
In the classical era, major empires involved in the Indian Ocean trade included the Mauryan Empire in India, the Han Dynasty in China, the Achaemenid Empire in Persia, and the Roman Empire in the Mediterranean. Silk from China graced Roman aristocrats, Roman coins mingled in Indian treasuries, and Persian jewels show up in Mauryan settings.
Another major export item along the classical Indian Ocean trade routes was religious thought. Buddhism, Hinduism, and Jainism spread from India to Southeast Asia, brought by merchants rather than by missionaries. Islam would later spread the same way from the 700s CE on.
During the medieval era, 400 - 1450 CE, trade flourished in the Indian Ocean basin. The rise of the Umayyad (661 - 750 CE) and Abbasid (750 - 1258) Caliphates on the Arabian Peninsula provided a powerful western node for the trade routes. In addition, Islam valued merchants (the Prophet Muhammad himself was a trader and caravan leader), and wealthy Muslim cities created an enormous demand for luxury goods.
Meanwhile, the Tang (618 - 907) and Song (960 - 1279) Dynasties in China also emphasized trade and industry, developing strong trade ties along the land-based Silk Roads, and encouraging maritime trade. The Song rulers even created a powerful imperial navy to control piracy on the eastern end of the route.
Between the Arabs and the Chinese, several major empires blossomed based largely on maritime trade. The Chola Empire in southern India dazzled travelers with its wealth and luxury; Chinese visitors record parades of elephants covered with gold cloth and jewels marching through the city streets. In what is now Indonesia, the Srivijaya Empire boomed based almost entirely on taxing trading vessels that moved through the narrow Malacca Straits. Even Angkor, based far inland in the Khmer heartland of Cambodia, used the Mekong River as a highway that tied it in to the Indian Ocean trade network.
For centuries, China had mostly allowed foreign traders to come to it. After all, everyone wanted Chinese goods, and foreigners were more than willing to take the time and trouble of visiting coastal China to procure fine silks, porcelain, and other items. In 1405, however, the Yongle Emperor of China's new Ming Dynasty sent out the first of seven expeditions to visit all of the empire's major trading partners around the Indian Ocean. The Ming treasure ships under Admiral Zheng He traveled all the way to East Africa, bring back emissaries and trade goods from across the region.
In 1498, strange new mariners made their first appearance in the Indian Ocean. Portuguese sailors under Vasco da Gama rounded the southern point of Africa and ventured into new seas. The Portuguese were eager to join in the Indian Ocean trade, since European demand for Asian luxury goods was extremely high. However, Europe had nothing to trade. The peoples around the Indian Ocean basin had no need of wool or fur clothing, iron cooking pots, or the other meager products of Europe.
As a result, the Portuguese entered the Indian Ocean trade as pirates rather than traders. Using a combination of bravado and cannons, they seized port cities like Calicut on India's west coast and Macau, in southern China. The Portuguese began to rob and extort local producers and foreign merchant ships alike. Scarred by the Moorish conquest of Portugal and Spain, they viewed Muslims in particular as the enemy, and took every opportunity to plunder their ships.
In 1602, an even more ruthless European power appeared in the Indian Ocean: the Dutch East India Company (VOC). Rather than insinuating themselves in to the existing trade pattern, as the Portuguese had done, the Dutch sought a total monopoly on lucrative spices like nutmeg and mace. In 1680, the British joined in with their British East India Company, which challenged the VOC for control of the trade routes. As the European powers established political control over important parts of Asia, turning Indonesia, India, Malaya, and much of Southeast Asia into colonies, reciprocal trade dissolved. Goods moved increasingly to Europe, while the former Asian trading empires grew poorer and collapsed. The two thousand year-old Indian Ocean trade network was crippled, if not completely destroyed.