Malaysia Day marks the joining of Malaya, North Borneo, Sarawak and Singapore to form Malaysia. This formation of the new federation was planned to occur on June 1, 1963, but was later postponed to August 31, 1963, in order to coincide with the sixth Hari Merdeka.
There was an Indonesian and Philippines objection to the formation of Malaysia which needed to be resolved and that delayed the declaration to September 16 of the same year. The postponement was also agreed to in order to allow the United Nations team time to conduct referendums in North Borneo (now Sabah) and Sarawak regarding the two states participation in a new federation.
Sarawak secured its independence on July 22 1963 while Singapore and North Borneo (now known as Sabah) declared independence from the United Kingdom on August 31, 1963, coinciding with the sixth anniversary of the Malayan independence.
Finally, the formation of Malaysia was made possible through the passing of the Malaysia Bill to the Malayan Parliament on July 9, 1963, and with the royal consent from the Yang di-Pertuan Agong, on August 29, 1963.
On a separate note, 9 August 1965, is the day the Parliament of Malaysia voted in favor of a constitutional amendment that will allow Singapore to exit from the federation. The Parliament of Singapore quickly passed the Republic of Singapore Independence Act, thus establishing the island as an independent and sovereign republic.
Beginning year 2010, September 16 is a federal public holiday where the whole of Malaysia celebrates as one. Happy Malaysia Day!!