"What were the principal causes of this political catastrophe? An early and continuing factor was the fiery rhetoric of Lee Kuan Yew and his decision to enter PAP candidates in the 1964 general election. Elections campaigns offer opportunities for the expression of intemperate opinions, which might otherwise remain unspoken. This rhetoric, admirably suited to the political scene in Singapore, soon antagonised Malayan leaders, including the ever-tolerant Tunku.
Lee told one rally that Tunku was not of the calibre to lead the nation. At another rally he told his audience: "We have to save the Tunku from his so-called friends", and at another, that "the Chinese leadership in the Alliance by the MCA is replaceable". There were also many other attacks on the MCA and attempts to split the UMNO-MCA alliance."
Above quote is taken from "Tunku, His Life And Times" (Mubin Sheppard, 2007, 230 pages), the authorised biography of Tunku Abdul Rahman, the man who had to fend off Macapagal of the Philippines and Sukarno of Indonesia to make Malaysia a reality.
After the 1964 election Tunku had to take action to de-escalate the incendiary atmosphere, and he arranged a meeting at which he, Tun Abdul Razak and Tan Siew Sin met Lee Kuan Yew, Lim Kim San and Dr Toh Chin Chye of the PAP to declare a truce, and agree not to raise sensitive issues relating to the position of the communities in Malaysia.
But by the middle of December 1964, inter-governmental co-operation between Singapore and the central government in Kuala Lumpur had deteriorated to such a serious extent that Tunku spoke of a "breakaway", and the calamity that would be for Singapore and Malaysia. Tunku's efforts at moderating was criticized by UMNO, and further jeopardised by a speech by Lee Kuan Yew on May 21, "If we must have trouble, let us have it now. If we find that Malaysia cannot work, then we can make alternative arrangements."
After recuperating from an attack of shingles in Switzerland, Tunku returned to Kuala Lumpur and wrote to British Prime Minister Harold Wilson, telling him that he and his ministers had decided on separation.
On evening of August 6, Goh Keng Swee and colleagues were in Kuala Lumpur and was told of the Alliance decision. Informed by telephone, Lee drove to see Tunku at about mid-day on Saturday, August 7. The congenial and kindly Tunku had run out of patience with the maverick, and produced the "Separation Agreement" for Lee to sign.
Ismail Kassim,of The Straits Times, Singapore, said in his review of the book, "It is a story that will strike a responsive chord in many readers... Not surprisingly, it abounds with many interesting vignettes about the personal life of the Tunku which are not generally known to the public." And not generally known to Singaporeans either.