There were only two men seriously considered to succeed Hammarskjold: Foreign Minister Mongi Slim of Tunisia and Ambassador U. Thant of Burma. Mongi Slim was soon dropped, for he was unacceptable to France — in the summer of 1961 French paratroopers had attacked the Tunisian city of Bizerte to maintain control of a naval base there, and relations with the Bourgiba government were strained. Paris was none too keen about Thant either, for he had chaired a UN committee on Algerian independence. In his memoirs, Thant recalled being asked by a correspondent about a French diplomat’s comment “that I was a ‘short man, and did not even speak French.’ É I told him that I was taller than Napoleon, and that he did not even speak English!”
But France was not the main problem; it was the Soviet demand that the Secretary-General be replaced by a “Troika” of officials, representing the capitalist, socialist and developing countries. After its experience with Trygve Lie in Korea and Hammarskjold — who it considered a “lackey of the imperialists” — in the Congo, Moscow scorned the idea of an impartial Secretary-General. But in the face of strong opposition, the Troika proposal was eventually given up. On 3 November 1961, Thant was made “Acting Secretary-General” to serve till April 1963, the end of Hammarskjold’s second term. At his request, he was then appointed Secretary-General to the end of 1966, in effect, giving him one full five-year term.
A few weeks before Thant became Secretary-General, he attended a meeting in Belgrade where 28 developing countries formally initiated the Non-Aligned Movement. Three years later, all 77 developing countries in the UN signed a declaration of shared interest and solidarity, creating the Group of 77. A “Third World” of poor countries was rapidly emerging on the "Cold War" scene, and their top priority, economic and social development, soon became that of the United Nations. The first Secretary-General to come from a developing country, Thant was finely attuned to the needs that had to be met. “I sometimes think the drafters of the Charter were overly obsessed with political and military conflict” he told UN correspondents in 1971, as his second term was coming to an end. “It might be useful to add an Article 99 (a) which would authorize the Secretary-General to bring to the attention of the membership global threats to human well-being other than those to peace and security. I have tried to do this without specific authorization, in matters such as population growth or the environment.” During his stewardship, there was unprecedented growth in the development apparatus of the UN. The most important additions were the UN Conference on Trade and Development (UNCTAD) in 1964 — its Geneva based secretariat serving as brains trust for the Group of 77 — and the UN Development Programme in 1965, to channel support for technical assistance. Other agencies established during that decade were the World Food Programme in 1963, the UN Industrial Development Organization in 1966, and the UN Population Fund in 1969. Two initiatives that Thant personally fostered came to fruition after he retired: the UN Environment Programme in 1972 and the UN University in 1973.
Meanwhile, there was no lack of political challenges. Potentially the most serious was the crisis over the clandestine Soviet effort to introduce nuclear missiles into Cuba in 1962. Thant’s face-saving intervention allowed Moscow and Washington to back away from suicidal conflict. On other issues — the continuing conflict in the Congo, civil war in Cyprus, international wars in South Asia and the Middle East, the US intervention in the Dominican Republic and the Soviet intervention in Czechoslovakia — the involvement of the United Nations and of the Secretary-General, varied enormously. Ambassador Arsene Usher of the Ivory Coast attempted a humorous codification of this variety during a Security Council discussion in 1965: “When there is a dispute between two small powers, the dispute eventually disappears. If there is a dispute between a small power and a great power, the small power disappears. And if there is a dispute between two great powers, the Security Council disappears.”
The Security Council effectively “disappeared” as a civil war in Viet Nam escalated in the 1960s into a long and brutal "Cold War" confrontation. As an Asian and as Secretary-General of an Organization in which neither part of Viet Nam was represented, Thant felt that he had to play some role, even though he had no mandate to do so and despite the fact that neither North Viet Nam nor the United States wanted the UN to be engaged. When quiet efforts to get negotiations under way failed, he decided to address the issue publicly. Washington’s intense irritation at his efforts led Thant to initially decline a second term, but after his right to seek a negotiated peace in Viet Nam was acknowledged publicly and in writing by the American Ambassador, he relented. Thant was an increasingly sick man during his second term and he died of cancer in 1974.