I slept well that night in my bedroom furnished in 19th Century style in the old French colonial hotel in Saigon. It had been a long and tiring previous day reporting on the war in the Delta of South Vietnam.

As I walked down the staircase towards breakfast, there was a young Indian gentleman standing near the reception desk. He was crying. His cheeks were shiny with tears and he held one hand partially over his face.

He was a Sikh, with a white turban and very handsome, with delicate features. I knew him slightly. He was an officer of the UN mission to Indo-China.

I went over. “What’s the matter? Can I help you?”

“You haven’t heard then.”

So I learned of the assassination of President Jack Kennedy far away in Dallas, Texas.

In an impassioned outburst, he said he had loved Kennedy as “the hope of the world.” He could not believe that anyone could kill him.

I went out on the terrace where we usually sat quietly, admiring the lovely young ladies of Saigon, walking past in their flowing white robes and conical hats.

That morning, there were angry American voices, a sense of how could this have happened in America. But the journalists hadn’t been able to find out much. There were a dozen theories about who had done it. One old journalist, known for his cynical comments, said” Well, it’s a bad year for presidents.”

The others looked at him angrily. But how extraordinary it was that Kennedy died only three weeks since the assassination of the President of South Vietnam, Ngo Dinh Diem. He had been killed by the Army just up the road in Saigon, but apparently with the silent support of American officials.

It was an immediate thought that maybe Diem’s friends or relatives had conspired to exact revenge. But that idea disappeared as one followed the long story of allegations and theories that have possessed Americans for fifty years.

I had found it hard to follow America’s role in those difficult times. There was the new American Ambassador to South Vietnam, Mr Henry Cabot Lodge Jnr. The appointment of this scion of upper crust society in the United States by a Democrat President was a surprise. Kennedy’s role in getting rid of Diem, a fellow Roman Catholic, is not known.

Lodge had arrived in Saigon only recently but had quickly made up his mind about Diem, according to American journalists I spoke with.

The year 1963 brought the situation to a head. Diem, a Roman Catholic, had attacked and suppressed the Buddhists, the great majority of people in South Vietnam, including giving preference to Catholics in the army. Buddhist priests had set fire to themselves in protest in the squares and streets of Saigon. The story and the shocking pictures went round the world.

But the question of dumping an ally in the midst of war has stuck in my mind. Later, we were to see the ignominious disappearance of the Americans from South Vietnam in 1975.

Getting rid of Diem was the big mistake the Americans made. Desperate attempts to find new leaders failed with a progression of army and air force generals who could not give national leadership. We learned that the Communist leader in Hanoi, Ho Chi Minh, was startled by the news of Diem’s death. He and his fellows thought Diem was the strong man who would be hard to defeat.

In recent times we have seen the Americans dump another ally, Hosni Mubarak, of Egypt, after 30 years. Professor Shlomo Avineri has reminded us that during those 30 years, Egyptians and Israelis were not killing each other.

Why not think back further to world war 11? Winston Churchill made Tito, the communist guerilla leader in Yugoslavia an ally and invited him to London. The Chinese Communist leaders, Mao Tse Tung and Chou En Lai, asked that they should come to Washington after fighting against the Japanese more effectively than the forces of Chiang Kai Shek. But the Americans declined, didn’t even pass on the request, and supported Chiang to defeat in the civil war, as historian Barbara Tuchman has told us (Notes from China 1972).