Before Indonesia's Confrontation of Malaysia, Sukarno had sought to develop an independent Indonesian foreign policy, focused on the acquisition of Netherlands New Guinea as a residual issue from the Indonesian National Revolution, and establishing Indonesia's credentials as a notable international power operating distinct interests from those of the West and East. Indonesia had relentlessly pursued its claim to Netherlands New Guinea during the period 1950–1962, despite facing multiple setbacks in the UN General Assembly to have its claim recognised by the international community. Indonesia was an important country in developing the Non-Aligned Movement, hosting the Bandung Conference in 1955.
Following the Indonesian crisis in 1958, which had included the Permesta rebellion in eastern Indonesia and the declaration of the PRRI, a rebel revolutionary government based in Sumatra; Indonesia had emerged as a notable and rising military power in Southeast Asia With the influx of Soviet arms aid, Indonesia was able to advance its diplomatic claims to Netherlands New Guinea more forcefully. The diplomatic dispute reached its climax in 1962 when Indonesia launched a substantial campaign of airborne and seaborne infiltrations upon Netherlands New Guinea. While the infiltration forces were soundly defeated by Dutch and indigenous forces, Indonesia was able to lend credence to the threat of an Indonesian invasion of Netherlands New Guinea. The Dutch, facing mounting diplomatic pressure from the Indonesians and the Americans, who were anxious to keep Indonesia from becoming Communist aligned, yielded and agreed to a diplomatic compromise, allowing the Indonesians to gain control of the territory in exchange for pledging to hold a self-determination plebiscite (the Act of Free Choice) in the territory by 1969. Thus by the close of 1962 Indonesia had achieved a considerable diplomatic victory, which possibly emboldened its self perception as a notable regional power. It was in the context of Indonesia's recent diplomatic victory in the Netherlands New Guinea dispute, that Indonesia cast its attention to the British proposal for a unified Malaysian state.
Prior to the British Government announcing the East of Suez policy in 1968, the British Government had begun to re-evaluate in the late 1950s its force commitment in the Far East. As a part of its withdrawal from its Southeast Asian colonies, the UK moved to combine its colonies in North Borneo with the Federation of Malaya (which had become independent from Britain in 1957), and Singapore (which had become self-governing in 1959). In May 1961, the UK and Malayan governments proposed a larger federation called Malaysia, encompassing the states of Malaya, North Borneo, Sarawak, Brunei, and Singapore. Initially, Indonesia was mildly supportive of the proposed Malaysia, although the PKI (Partai Komunis Indonesia — Indonesian Communist Party) was strongly opposed to it.
In Brunei, it was unclear whether the Sultan Omar Ali Saifuddien III would support Brunei joining the proposed Malaysian state because of the implied reduction of his political office, and Brunei's oil revenues ensured Brunei's financial viability were it to choose independence. Furthermore, a Brunei politician, Dr. AM Azahari bin Sheikh Mahmud, while supporting a unified North Borneo, also opposed a wider Malaysian federation. In 1961, he had sounded out Indonesia about possible aid in training Borneo recruits; General Abdul Nasution hinted at moral support, and Soebandrio, the Indonesian foreign minister and head of intelligence, hinted at supplying more substantial aid. Azahari was a leftist who had fought in Indonesia in their war for independence. Following these meetings Indonesia began training in Kalimantan a small volunteer force, the North Kalimantan National Army (TNKU).
On 8 December 1962, the TNKU staged an insurrection—the Brunei Revolt. The insurrection was an abject failure, the poorly trained and equipped forces were unable to seize key objectives such as capturing the Sultan of Brunei, seize the Brunei oil fields, or take European hostages. Within hours of the insurrection being launched, British forces based in Singapore were being mobilised for a prompt response. The failure of the insurrection was clear within 30 hours when Gurkha troops airlifted from Singapore secured Brunei town and ensured the Sultan's safety.
The degree of Indonesian support for the TNKU remains a subject of debate. While Indonesia at the time denied direct involvement, it did sympathise with the TNKU's objectives to destabilise the proposed Malaysian state. Following the TNKU's military setback in Brunei, on 20 January 1963 Indonesian Foreign Minister Subandrio announced that Indonesia would pursue a policy of Konfrontasi with Malaysia, reversing Indonesia's previous policy of compliance with the British proposal. This was followed by the first recorded infiltration of Indonesian forces on 12 April 1963 when a police station in Tebedu, Sarawak, was attacked.
People and terrain
In 1961, the island of Borneo was divided into four separate states. Kalimantan, comprising four Indonesian provinces, was located in the south of the island. In the north, separated from Kalimantan by a border some 1000 miles long, were the Sultanate of Brunei (a British protectorate) and two colonies of the United Kingdom (UK)—British North Borneo (later renamed Sabah) and Sarawak.
Borneo today; divided between Brunei, Indonesia and Malaysia. The control of the island was the main issue behind the war at the time.
The three UK territories totaled some 1.5 million people, about half of them Dayaks. Sarawak had a population of about 900,000, while Sabah's was 600,000 and Brunei's was around 80,000. Among Sarawak's non-Dayak population, 31% were Chinese, and 19% were Malay. Among non-Dayaks in Sabah, 21% were Chinese and 7% were Malay; Brunei's non-Dayak population was 28% Chinese and 54% Malay. There was a large Indonesian population in Tawau in southern Sabah and a large and economically active Chinese one in Sarawak. Despite their population size, Dayaks were spread through the country in village longhouses and were not politically organised.
Sarawak was divided into five administrative Divisions. Sabah, whose capital city was Jesselton (Kota Kinabalu) on the north coast, was divided into several Residencies; those of the Interior and Tawau were on the border.
Apart from either end, the border generally followed a ridge line throughout its length, rising to almost 2,500 metres in the Fifth Division. In the First Division, there were some roads, including a continuous road from Kuching to Brunei and around to Sandakan on the east coast of Sabah. There were no roads in the Fourth and Fifth Divisions or the Interior Residency, and in Third Division, there was only the coast road, which was some 150 miles from the border. Mapping was generally poor, as British maps of the country showed very little topographic detail. Indonesian maps were worse; veterans recall "a single black and white sheet for all of Kalimantan torn from a school text book" in 1964.
Kalimantan was divided into four provinces, of which East Kalimantan and West Kalimantan face the border. The capital of the West is Pontianak on the west coast, about 100 miles (160 km) from the border, and the capital of the East is Samarinda on the south coast, some 220 miles (350 km) from the border. There were no roads in the border area other than some in the west, and no road existed linking West and East Kalimantan.
The lack, on both sides of the border, of roads and tracks suitable for vehicles meant that movement was limited to foot tracks mostly unmarked on any map, as well as water and air movement. There were many large rivers on both sides of the border, and these were the main means of movement, including hovercraft by the UK. There were also quite a few small grass airstrips suitable for light aircraft, as dropping zones for parachuted supplies, and for helicopters.
The equator lies about 100 miles south of Kuching, and most of northern Borneo receives over 3000 mm of rain each year. Borneo is naturally covered by tropical rainforest. This covers the mountainous areas cut by many rivers with very steep sided hills and hilltop ridges often only a few metres wide. The high rainfall means large rivers; these provide a main means of transport and are formidable tactical obstacles. Dense mangrove forest covering vast tidal flats intersected with numerous creeks is a feature of many coastal areas, including Brunei and either end of the border. There are cultivated areas in valleys and around villages. In the vicinity of abandoned and current settlements are areas of dense secondary regrowth.
The end of the Second World War had brought an end to the Brooke Dynasty rule in Sarawak. Believing it to be in the best interest of the people of Sarawak, Charles Vyner Brooke ceded the state to the British Crown. Sarawak became a Crown colony, ruled from the Colonial Office in London, which in turn dispatched a governor for Sarawak.
The predominantly Malay anti-cession movement, which rejected the British takeover of Sarawak in 1946 and had assassinated Duncan Stewart, the first British High Commissioner of Sarawak, may have been the forerunner of the subsequent anti-Malaysia movement in Sarawak, headed by Ahmad Zaidi Adruce.
According to Vernon L. Porritt and Hong-Kah Fong, Left-wing and communist cell groups had been present among Sarawak's urban Chinese communities since the 1930s and 1940s. Some of the earliest Communist groups in Sabah included the Anti-Fascist League, which later became the Races Liberation Army, and the Borneo Anti-Japanese League, which was made up of the North Borneo Anti-Japanese League and the West Borneo Anti-Japanese League. The latter was led by Wu Chan, who was deported by the Sarawak colonial government to China in 1952. Other Communist groups in Sarawak included the Overseas Chinese Youth Association, which was formed in 1946, and the Liberation League along with its youth wing, the Advanced Youth Association, which emerged during the 1950s. These organisations became the nuclei for two Communist guerilla movements: the anti-Malaysia North Kalimantan People's Army (PARAKU) and the Sarawak People's Guerrillas (PGRS). These various Communist groups were designated by various British and other Western sources as the Clandestine Communist Organisation (CCO) or the Sarawak Communist Organisation (SCO).
Members of the Sarawak People's Guerilla Force (SPGF), North Kalimantan National Army (NKNA) and Indonesian National Armed Forces
(TNI) taking photograph together marking the close relations between them during Indonesia under the rule of Sukarno
The Sarawak Communist Organisation, was predominantly dominated by ethnic Chinese but also included Dayak supporters. However, the Sarawak Communist Organisation had little support from ethnic Malays and other indigenous Sarawak peoples. At its height, the SCO had 24,000 members. During the 1940s and 1950s, Maoism had spread among Chinese vernacular schools in Sarawak. Following the Second World War, Communist influence also penetrated the labour movement and the predominantly-Chinese Sarawak United People's Party, the state's first political party which was founded in June 1959. The Sarawak Insurgency began after the Brunei Revolt in 1962 and SCO would fight alongside the Bruneian rebels and Indonesian forces during the Indonesia–Malaysia confrontation (1963–1966).
The Sarawak Communist Organisation and the Bruneian rebels supported and propagated the unification of all British Borneo territories to form an independent leftist North Kalimantan state. This idea was originally proposed by A. M. Azahari, leader of the Parti Rakyat Brunei (Brunei People's Party), who had forged links with Sukarno's nationalist movement, together with Ahmad Zaidi, in Java in the 1940s. However, the Brunei People's Party was in favour of joining Malaysia on the condition it was as the unified three territories of northern Borneo with their own sultan, and hence was strong enough to resist domination by Malaya, Singapore, Malay administrators or Chinese merchants.
The North Kalimantan (or Kalimantan Utara) proposal was seen as a post-decolonisation alternative by local opposition against the Malaysia plan. Local opposition throughout the Borneo territories was primarily based on economic, political, historical and cultural differences between the Borneo states and Malaya, as well as the refusal to be subjected under peninsular political domination. Both Azahari and Zaidi went into exile in Indonesia during the confrontation. While the latter returned to Sarawak and had his political status rehabilitated, Azahari remained in Indonesia until his death on 3 September 2002.
In the aftermath of the Brunei Revolt, the remnants of the TNKU reached Indonesia. Possibly fearing British reprisals (which never eventuated), many Chinese communists, possibly several thousand, also fled Sarawak. Their compatriots remaining in Sarawak were known as the CCO by the UK but called the PGRS—Pasukan Gelilya Rakyat Sarawak (Sarawak People's Guerilla Force) by Indonesia. Soebandrio met with a group of their potential leaders in Bogor, and Nasution sent three trainers from Resimen Para Komando Angkatan Darat (RPKAD) Battalion 2 to Nangabadan near the Sarawak border, where there were about 300 trainees. Some 3 months later two lieutenants were sent there.
The PGRS numbered about 800, based in West Kalimantan at Batu Hitam, with a contingent of 120 from the Indonesian intelligence agency and a small cadre trained in China. The PKI (Indonesian Communist Party) was strongly in evidence and led by an ethnic Arab revolutionary, Sofyan. The PGRS ran some raids into Sarawak but spent more time developing their supporters in Sarawak. The Indonesian military did not approve of the leftist nature of the PGRS and generally avoided them.