Asia did not adopt the caste system, nor even the dietary habits of the Indians like curry powder or milk products. Politically, none of the supposed Southeast Asia 'colonies' showed any allegiance to India. Economically speaking, the states of Southeast Asia were not colonies as there was no scope of economic exploitation. India also did not enjoy monopoly in the field of foreign trade.
The absence of concrete evidence regarding Indian cultural expansion has resulted in the postulation of various theories regarding the motives and the process of the transfer of Indian cultural elements to Southeast Asia. In this article, the flow of Indian cultural elements is shown in the context of Southeast Asian initiative or 'indigenization'. The consensus is that the process of Indian cultural expansion in Southeast Asia was accomplished by peaceful means and it was non-political in character. There is first the kshatriya (warrior class) theory, which presupposes that Indian cultural expansion was due to the seminal influence of the Indian warriors and conquerors, who migrated in large numbers to Southeast Asia. The vaisya (merchant class) theory postulates that Indian cultural penetration began with traders, who intermarried with local women and impressed the indigenous population with their goods and culture. The third theory, commonly known as brahmana (priestly class) theory accorded primacy to local initiative: indigenous port patricians and rulers enlisted the service of brahmans to buttress their political authority through Hindu ceremonies and rituals. Rather than being the result of a single factor, most likely the whole process of Indian cultural expansion was the outcome of endeavors of warriors, traders and priests along with the indigenous initiative. Most probably all four groups of people were involved in the process.
One of the significant factors in the spread of Indian cultural influence in Southeast Asia is geographical proximity between two regions. The fabulous wealth of Southeast Asia was an attraction for the Indians. The type of names given to different regions of Southeast Asia is recognition of this desire for economic gain. The Ramayana, Pali Nidesa and other works refer to Suvarnabhumi (land of gold), Suvarnadvipa (island of gold), Narikeladvipa (island of coconuts), Karpuradvipa (island of camphor), and Yavodvipa (island of barley). In respect of kingdom of P'an-p'an, it has been said that the numerous brahmans of that kingdom came from India in search of wealth. Inscriptions attest to the arrival of Indian brahmans to Cambodia and settling there after marrying in royal families. The missionary activities of Buddhists also resulted in large number of Indians settling in the region.
Although the most intensive cultural contact between India and Southeast Asia came in later centuries, initial contact between the two regions dates to prehistoric times. There was racial and linguistic affinity between certain groups of people of eastern India with Southeast Asians. Archaeological excavations are also a testimony of the interaction between the two regions. In the Korat plateau of Thailand, glass and stone beads have been found, which was an indicator of trade contact with India. Ban Chiang in Thailand had yielded bimetallic spearheads belonging to first millennium BCE. The same types of artifacts have been reported from places like Mahurijhari in Madhya Pradesh, Gilmanuk in Bali, Prajekan in Java and Dongson in Vietnam. The Buni complex in Java hadyielded Indian rouletted ware of the first and second centuries CE. Sembrian in Bali is another site, whose finds include sherds of pottery of types found at Arikadmedu, an important Indo-Roman trading center. An Indian type of gold foil funerary eye cover had been recovered from the site of Gilimanuk. In Oc Eo in Vietnam, which was an entrepôt from the second century CE onwards, finds have included items like beads, intaglios and seals with Sanskrit inscriptions. Therefore, the early centuries of the common era saw a greater impetus in the direction of Indo-Southeast Asian relations.
In the spread of Indian culture, the sea played an important role. There was intensification of sea-borne commerce in the early centuries of Common Era. Along with traders, missionaries, priests, literati, adventurers and fortune seekers went to Southeast Asia. The ancient port of Tamralipti at the mouth of Ganga was one of the earliest places of embarkation. From there, ships proceeded to the Malay Peninsula either along the coasts of Bengal and Myanmar or through the Bay of Bengal. Chinese texts of the third century CE attest to this fact. A trader from western India reached what the Chinese called Funan in the second century CE, and the Funanese king Fan Chen, after learning from the trade about India, sent one of his relations there. The latter embarked at Teu-ki-li, reached the mouth of Ganga and proceeded further. Ships from the Mediterranean visited this port of Tamralipti, which was situated at the extremity of Orissa's domain. From there, vessels then sailed to Southeast Asia and China. After the decline of Indo- Roman trade, the route from India to China through Southeast Asia did not cease. Ptolemy had referred the port of Palura as an apheterion, where the ships ceased to follow the coastal littoral and entered the high seas. Palura was the port of departure for Roman ships before sailing to Southeast Asia and, afterwards, to China. The ships reached Aden from Egypt and arrived at the coast of India. From Arikamedu the ships sailed to Palura and reached Arakan through Bay of Bengal. They went south along the coast to the delta of Irrawaddy and then turned into the Gulf of Martaban. The ships reached the port of Oc Eo after passing through Takkola, Klang and Pattani. Final destination was the port of Kattigara. The traders avoided the risky sea route round the coast of Malay Peninsula. They went to Thailand through Kedah and took the land route to Campa after crossing Laos and Cambodia.
During the early centuries of common era, trade with China through Southeast Asia followed two routes. The first was from the Andhra and Kalinga coast, from where the ships went to Irrawaddy valley of Myanmar after crossing the Bay of Bengal. From the valley, the traders went to the upper Yangtse basin through Salween and Mekong rivers. The second route started from Tamralipti, reached Sri Lanka and sailed directly through the Nicobar islands either to the Sunda straits or straits of Malacca. From places like lower end of Sumatra or western end of Java, it was easy to go up the Malay coast past Pattani, Singora and Ligor to the port of Oc Eo. The voyage then covered the coast past Campa to Chio-Chi port in Vietnam or on to Canton. After reaching the ports of Malay, the Indian sailors went either through the pirate-infested straits of Melaka (Malacca) or safer land route to the east coast. Across the narrow Isthmus of Kra, from Takupa on the western side to Chaiya on the eastern, there was a short cut. Another route was from Tavoy over the three pagodas pass and then by Kanburi river to the valley of Menam. Still there was another passage connecting the Menam region to the Mekong by way of the Korat plateau via Sri Tep and the Mon valley. It is not surprising that some of the places mentioned above are archaeological sites and places of Indian influence. The monsoon wind played a major role in determining the maritime operations on the Bay of Bengal. As the southwest monsoon during April to October caused adverse weather conditions in the straits, sailors preferred northeast monsoon at the time of October to April for starting their journey from India. The ships sailing from China would come to the straits on the northeast monsoon and up the straits in time for the next northeast monsoon to sail to India.
Apart from Arikamedu, Palura and Tamralipti, there were other ports on the eastern coast of India: Masulipatnam (Machhlipatna), Kamana (Kalapattana), Poduke (Pondicherry), Supatana (near Chennai), and Puhar (Kaveripattanam). On the west, following the nomenclature of Periplus, there were, on the mouth of Narmada, Barygaza (Broach), Suppara (Sopara), Calliena (Kalyan), Semylla (Chaul), and Naura (Cannanore). Another work, the Milindapanha (Questions of King Milinda) of the first century CE refers to the name of places in India and Southeast Asia and mentions the name of important ports like Sovira (lower Indus valley), Suratta (Gujrat), Cola Pattana (Coromandel Coast), Vanga (Bengal), and Suvarnabhumi (lower Myanmar). The ports also played an important role as diffusion centers for Indian art elements to Southeast Asia. The port of Amaravati at the lower reaches of Krishna River was not far from Palura. Sailing from the ports of Palura-apheterion complex, the early Buddhist missionaries and migrants carried with them the sculptures of Amaravati school of art. The images of this school have been found in various places in Southeast Asia: Palembang, east Java, West Celebes, Korat, and Dong Duong. Spots from where these sculptures have been found are situated on the sea-route taken by Su-wu in the middle of the third century CE.
In the whole gamut of Indo-Southeast Asian relations, both Indians and Southeast Asians played an active role. Apart from movement of people and racial and linguistic affinity, there were also trading relations. Along with traders, brahmans (priests) from India came to Southeast Asia, who acquainted the local elite with Indian rituals, scriptures, and literature. They became counselors in the affairs of the courts and provided political support to the rulers by giving them a sort of investiture and genealogical list, which legitimized the position of rulers. Indian elements like Sanskrit language, the Hindu-Buddhist cults, Dharmashastras, and the Indian concept of royalty became essential features of the early states of Southeast Asia.