Singapore, officially the State of Singapore, was briefly one of the 14 states of Malaysia from 1963 to 1965. Malaysia was formed on 16 September 1963 by the merger of the Federation of Malaya with the former British colonies of North Borneo (Sabah), Sarawak and Singapore. This marked the end of 144 years of British rule in Singapore, which began with the founding of modern Singapore by Stamford Raffles in 1819. With a land area of approximately 670 km (260 sq mi), it was the smallest state but had the largest population and was highly urbanised, playing a central role in the national economy. As part of the integration referendum and the Malaysia Agreement, Singapore was given autonomous status including in education, labour and healthcare.
The merger was supported by the British, Malayan and Singaporean leaders as a measure to counter the influence of communism in Southeast Asia, especially through the Malayan Communist Party (MCP). The threat of communist expansion was considered serious by all parties, and the union was seen as a means to contain it through political consolidation. However, serious disagreements soon surfaced between the governments of Singapore and Malaysia, led by the People's Action Party (PAP) and the Alliance Party respectively. Conflicts arose over financial contributions, political participation and racial policies. Although a common market had been promised in exchange for Singapore's substantial tax revenues, trade barriers remained in place. In response, Singapore withheld development loans to Sabah and Sarawak. The situation was worsened when the Malay–based United Malays National Organisation (UMNO) of the Alliance and the PAP contested elections beyond their agreed jurisdictions, triggering further mistrust.