Defined as the region of land between India to the west, China to the north, and the Pacific Ocean to the east, Southeast Asia today comprises 10 countries: Brunei, Cambodia, Indonesia, Laos, Malaysia, Burma, the Philippines, Singapore, Thailand (Siam), and Vietnam.

Allah Almighty speaks of traveling to different lands in the Qur’an. Today we find the essential foundations of faith in all Muslim countries, yet we have regional interpretations, from the apparently traditional interpretation found in rural Thailand to the dynamic face of Islam in Singapore. Thus while we can trace the route of Islam when it spread into certain countries, we can also see how the synthesis of pre-Islamic regional culture and the teachings of Islam created different communities, all of which share the same common foundations.

From the early days of Islam we know of two routes eastwards: the land route and the sea route to China which, for example, the uncle of the Prophet Muhammad (peace be upon him) Saad ibn Abi Waqqas sailed.

Accounts of how Islam spread to this region vary according to different translations. Credit should be given to Professor Masud ul-Hassan, whose large text History of Islam, Vol. II, I used as a primary source.

Vietnam: 11th Century
The Kingdom of Chams flourished in Vietnam until the 17th century. Between 1607 and 1676 the King of Champa accepted Islam. The area where the king and his settlers lived is known as Kompong Cham and they settled along the Mekong River in Vietnam in a group of 13 villages. Throughout this period the children would be sent to Kelanten (Malaysia) to study the Qur’an and Islamic studies, and would return to teach others in their village.
 
During the 17th century the Champa provinces were gradually conquered by the Vietnamese. The Vietnamese king Minh Mong persecuted the Champa, as a result of which the Champa Muslim king Po Chen gathered his people. Those on the mainland migrated to Cambodia, and those in the coastal provinces migrated to Trengannu (Malaysia).
 
However, not all of the Muslims migrated; some chose to stay in the central provinces of Vietnam such as Nha Trang, Phan Rang, Phan Ri, and Phan Thit. Because of their isolation from other Muslim communities, their Islam was strongly influenced by Hinduism and Buddhism, and their descendants over time lost the Islam which originally came to Vietnam.
 
Speaking of the early trade routes, Hourani observed that the people of Vietnam were exposed to Muslim traders in the 7th century:

After the passage through the Malacca Strait, known to the Arabs by its Malay name of Salaht (“Strait”), a call was made at Tiuman Island. Next cutting across to Indo-China, they stopped at ports in Sanf, the Champa kingdom in the eastern coastal, then at an island off the coast, known as Sanf Fulaw (corrupted in our texts to “Sandar Fulat”). From there vessels might coast round the Gulf of Tongking to Hanoi, known as Luqin, before they made for their final destination, Canton, which was called Khanfu.
Maspero opined that some Champa had already accepted Islam towards the end of the Sung dynasty from the 10th to the 11th century. Recent excavations have uncovered two gravestones of Champa Muslims with Kufic inscriptions dating back to 1030, which suggest that there existed a Muslim Champa community in the 10th century.

Malacca: 1400–1511
The first Muslim state to be established on the Malayan mainland was the state of Malacca. By the end of the 14th century, Parmeswara, a prince of the Hindu state of Mujaphait in Indonesia, migrated to Malaya and captured the island of Tumasik, turning it into a pirate base from where to attack ships. Ejected from Tumasik by the Siamese who controlled the area, Parmeswara settled in Malacca, which grew from a small fishing village to a major port. As Siam was hostile to Parmeswara, he sought the protection of the Chinese and established cordial relations with the neighboring states of Sumatra. Parmeswara married a Muslim princess of the state of Samudra Pasai in Sumatra and accepted Islam, adopting the name Muhammad Iskandar Shah. Islam thus came to Malaya in the 15th century, and Iskandar Shah died in 1424.
 
Iskander Shah was succeeded by his son Sri Maharaja, who ruled for 20 years. When he died, he left two sons: Raja Kassim and Dewa Shah. With the help of Malayan chiefs, Dewa Shah took authority but was overthrown by his brother Raja who, upon taking office, took the name Muzaffar Shah. Under his authority Islam became the state religion.

Threatened by the growing commercial strength of Malacca, Siam attacked it by land and sea. When this failed, Siam made peace with Malacca by recognizing its independence. Muzaffar Shah ruled for 15 years and died in 1459. His son Manzur Shah took over, and it was under his authority that Malacca expanded, conquering the neighboring states of Pahang, Perak and Kelentan. In the south, Johore and the islands adjoining the peninsula were brought under Malaccan control. Campaigns were then taken against Sumatra and the states of Batak, Kokan, Siak, Kampar, Indiragiri, and Jambi.

Manzur Shah took steps to promote Islam, and Malacca became the center from which Islam spread into Southeast Asia. He ruled for 18 years and died in 1477, by which time Malacca had become the strongest state in Southeast Asia.
 
Manzur Shah was succeeded by his son Alauddin Riyat Shah. He adorned Malacca with various public buildings and further expanded the dominion of Islam, spreading to Java, Sundar, the Molucass, Brunei, and the outlaying islands of Sumatra. He ruled for 11 years and died in 1488.

Alauddin was followed up by his son Mahmud Shah. He lacked the vision of his father and grandfather, so authority was managed by the chief minister. The Portuguese arrived in Malacca in 1509 under the auspices of trade, but merchants from Goa, India, warned the Malaccans of the Portuguese’ intention. They left unsuccessful. In 1510 Mahmud Shah had his chief minister killed, which act led to a state of chaos. The Portuguese exploited this opportunity, invaded, and captured Malacca in 1511.

Aceh: 1514–1599
After the occupation of Malacca, the next Muslim state to rise was Aceh in the western part of Sumatra, in 1514, with a union between the principalities of Lamri and Aceh Darl-ul-Kamal, under the authority of Ali Mughayat Shah.
 
In 1524 Ali captured Pasai from the Portuguese, and the state of Aceh then included most of the territories formerly under the state of Sumatra Pasai. When Malacca on the mainland was captured by the Portuguese in 1517, it became inaccessible to Muslim merchants and business shifted to Aceh, turning it into an extremely prosperous region. Aceh thus became a rival power to the Portuguese in Southeast Asia.

Ali is noted as one of the greatest rulers of the 16th century. Not only was his rule mild and just, but he maintained a strong army and navy. He encouraged the teaching of Islam, and it was under his rule that the religion spread from the coastal areas into the mainland. His rule lasted for 34 years and he died in 1548.

Ali was succeeded by his son Alauddin Shah, under whose rule Aceh expanded to include Aru and Johore on the mainland. Alauddin established good relations with the Ottoman Turks and received their help to obtain large guns. Heavily armed, he took to recapturing Malacca from the Portuguese but failed. He ruled for 23 years and died in 1571.

When Ali died, he was succeeded by his son Ali Hayat Shah, whose rule lacked vision. Ali Hayat died in 1579 and was succeeded by three equally poor rulers, one after another, until 1588. Order was returned to the area with the rule of Alauddin Rayat Shah, who reorganized the administration and ruled with justice.

Demak: 15th–16th Century
Java is the central island of Indonesia. Islam first spread to Sumatra in the 13th century, and later in the 14th century it spread from Sumatra to Java. The Gujurat style tomb of Malik Ibraham, a da`i who died in 1419, can be found there. Another tomb that can be found there is that of Princess Champa, who died in 1448. She was the wife of the ruler of Majaphit, a Hindu state that was the dominant power of Java. As a Muslim woman she was unable to marry a non-Muslim man, so it seems that the ruler of Mujaphait accepted Islam, although his successors were Hindus.
 
Chinese accounts show that during the early years of the 15th century, the population of Java comprised Muslims, Chinese, and Hindus. The Muslims lived in the coastal towns. Most of the Chinese were Muslims, but the majority of people were still Hindus.

The first Muslim state in Java was the state of Demak, established around 1500 by a warrior called Radhan Paria. Radhan conquered Cheribon and some neighboring islands, and then went on to south Sumatra, capturing Palembang and Jabi. In 1511 Radhan headed a campaign against the Portuguese in Malacca but failed. Instead he directed his efforts to the Indian state of Mujaphait and in 1527 overthrew its last ruler. Radhan died shortly thereafter, having turned Demak into the most dominant power in Java.

Radhan was succeeded by Trengganu, under whose authority the state of Demak gained further importance. He overpowered the states of Mataram and Sanda Kalappa, and under his authority Islam spread to the mainland of Java. While Radhan had previously conquered Mujaphait, he did not completely remove Hindu rule; thus a new, smaller state arose, and at the battle of Panarukan, Trengganu died.

After his death a state of confusion spread in Demak, causing the state to divide into two principalities, one with the capital Demak, the other with the capital Padong. As a result the state lost its importance. In 1578 the ruler of Padong conquered Demak. Yet despite the union, Demak was unable to reclaim its previous glory. In 1586, the Sultan of Demak was overthrown by his commander in chief, who founded a new Muslim state, Mataram.
 
Southeast Asian Islands: 15th–17th Centuries
The Moluccas: In the Moluccas, now referred to as the Spice Islands, Islam spread during the late 15th century. The first Muslim ruler was Zain-ul-Abdin, who ruled from 1486 to 1500. The Portuguese settled on the island in the 16th century and tried to convert people to Christianity. The people, however, chose Islam. Zain-ul-Abdin is said to have built a seven-story mosque in Ambon.
 
Celebes: Islam spread to Celebes in the early 17th century. The Prince of Tallo accepted Islam in 1605, after which he expanded his territory to the states of Bone, Coppeng, and Wajo, where the people accepted Islam. It was the Muslims of Celebes who played an important role in the battle against the Dutch in the Moluccas. When the Portuguese conquered Ambon, the Muslims fled to Makasar. The Muslims of Celebes fought against the Dutch East India Company for many years, resulting in the treaty of Bongeaid in 1667 through which the Dutch gained authority and Makasar lost its importance.

East Borneo: Islam spread from Celebes through the preaching of two Muslim da`is—Datori Bandang and Tuan Tunggang Parangan—who arrived at Kutei and converted the king, the princes, and the people to Islam. The king married a Muslim princess from Java and established a series of mosques and schools to teach Islam.
 
In the early 16th century, Bandjarmasin was the main kingdom of South Borneo. A dispute arose between two princes, Samudra and Tumengung, both of whom aspired to the throne. During the conflict Samudra sought the assistance of the Muslim state of Demak in Java. Demak promised assistance on the condition that Samudra would accept Islam. Samudra agreed. Demak assisted him to take rule, and he accepted Islam, after which his people also converted.

Brunei: Islam spread through northwest Borneo in the 15th century. The first Muslim ruler of Brunei was Awang Alakber Tabar, who took the name Muhammad when he accepted Islam. He married a Muslim princess from Johor. Throughout the 15th century, Brunei was overshadowed by the powerful state of Malacca. When the Portuguese conquered Malacca in 1511, many Malaccan Muslims migrated to Brunei, raising Brunei’s importance.

When Magellan sailed to Brunei in 1521, his Italian captain, Pigafella, wrote an account of the voyage. According to this report, the Sultan of Brunei was a man named Bulkiah who lived in a fortified residence surrounded by a brick wall on which fifty canons were mounted. Through its effective administration, the rule of Brunei was extended to the greater part of Borneo and even to the Sulu islands.

During the 16th century, the Spanish spread their influence to the Philippines and then pushed southwards, which caused Brunei to lose control over its lands. When the Dutch occupied south Borneo, Brunei was confined by the Spanish and the Dutch and became the small area to the northwest of Borneo. The Dutch trade monopoly strangled trade with Brunei, and by the 17th century Brunei was known for its piracy.

Sulu Islands: Islam spread to these islands through two da`is: Sharif Karim Al-Makhdum and Abu Bakr. The prince of Bawansa, Rafa Bainda, was the first ruler of the islands to accept Islam. Abu Bakr married one of his daughters and succeeded his father-in-law to the throne of Bawsana.

The Philippines: Islam came to these islands by way of Sharif Kabungsuwam. He came from Johor and settled in Mindanao, where many people accepted Islam. When the Spanish came to the Philippines, they resisted the spread of Islam to Manila. War broke out between the Muslims (Moros) and the Spanish, which lasted over a hundred years; the Muslims were unable to gain political authority but were nonetheless strong enough not to be expelled from the islands.

References:
Ul-Hassan, Masud. History of Islam, Vol. II. Islamic Publications, 1998.
Hourani, George. Arab Seafaring. Princeton University Press, 1979.
Maspero, Rene Gaston Georges. The Champa Kingdom: The History of an Extinct Vietnamese Culture, 1928. Cited by Pierre Yves Manguin, “The Introduction of Islam into Champa,” JMBRAS, Vol. LVIII, Part 1, 1985.
The Spread of Islam in Southeast Asia. Map. The Applied History Research Group, University of Calgary.

Source : http://islamonline.net