The Federation of Malaysia, comprising the States of Malaya, North Borneo (later renamed Sabah), Sarawak and Singapore was to be officially declared on the date August 31, 1963, on the 6th anniversary of Malayan independence. However, it was postponed to September 16, 1963, mainly due to Indonesian and the Philippines' opposition to the formation of Malaysia. Nevertheless, North Borneo and Singapore declared sovereignty on August 31, 1963. Indonesian opposition later escalated to a military conflict. Indonesia considered Malaysia as a new form of colonization on the provinces of Sarawak and Sabah in the island of Borneo (bordering Kalimantan, Indonesia), which they laid claim on. To assure Indonesia that Malaysia was not a form of neo-colonialism, a referendum, organized by the United Nations, and the Cobbold Commission, led by Lord Cobbold, were formed to determine whether the people of Sabah and Sarawak wished to join Malaysia. Their eventual findings which indicated substantial support for Malaysia among the peoples of Sabah and Sarawak, cleared the way for the final proclamation of Malaysia.
The formation of the Federation of Malaysia was then announced on September 16, 1963 as Malaysia Day. The nationwide Independence Day celebration is still held on August 31, the original independence date of Malaya, while Malaysia Day is a public holiday only in East Malaysia. However, this has caused some minor discontent among East Malaysians in particular since it has been argued that celebrating the national day on August 31 is too Malaya-centric It is decided that starting 2010, Malaysia Day will be a nationwide public holiday in addition to Hari Merdeka on August 31.