I have a confession to make: as I stood for the American national anthem during President Barack Obama's address to the Ghana Parliament on 11 July 2009, I felt the pleasing sensation of being present at a momentous moment in human history.

Formerly, when I heard the US national anthem, I sneered, for whereas great athletes like Jesse Owens and Carl Lewis had advertised American prowess world-wide, they were largely relegated to – in the words of Malcolm X – "the back of the bus" when they returned to the US. But there, in Accra, the anthem was being played for America's No 1 citizen. And he was black.

He had brought Air Force One to Accra. The US Secret Service was all over the place, making Ghanaians wonder when their independence took flight. Yet no one felt any resentment. For the President of the US was one of us.

As the helicopter took off from Accra, women, clad in special colourful cloths displaying a huge image of a smiling Obama, waved flags and sang. I asked, "What are you singing?"

They said: "We are singing: 'Obama do something before you go!'"

In that single line was the message in the heart of almost every African who has been gladdened by the election of a black man to be President of the United States. The message is that Obama should not let his presidency be an irrelevant diversion, which, while creating friendship for the United States in Africa, nevertheless leaves the continent in the poverty and misery that have been its lot for the past 100 years.

In the speech that Obama made to Ghanaian Parliamentarians and which has been reinforced by his Secretary of State, Hillary Clinton, in the seven-country visit she has just made to Africa, the administration shows little awareness of the real reason why Africa's economy has been stagnating.

They both emphasised the need for Africa to eliminate corruption and bad governance from its political system, and they are right. But what they left unanswered is this: After Africa eliminates corruption and practices good governance, then what?

The answer lies in these words: adding value to African raw materials before export. First, Africa should be allowed, through the abolition of the tariff walls erected by members of the G8 group of industrialised nations against its manufactured goods, to earn a lot more money from its exports. Coffee, for instance, is the second largest traded commodity in the world, second only to oil. Yet the coffee shops of the West take about 98 per cent of the income from the crop, leaving coffee farmers with a meagre 2 per cent.

This situation can be extrapolated to apply to cocoa, tea, cotton, timber, and – especially – to minerals like copper, iron, tin, bauxite and manganese. Even gold and diamonds are exported unprocessed from Africa, though African artistry in jewellery-making has astounded the world, with beautiful products from the days of Tutankhamun, to the Ashanti, kingdom of gold.

If Obama could use his position as leader of the West to advocate that the G8 establish an African Empowerment Fund, which would lend money cheaply to African countries that want to process their raw materials before export, and couple that with an assault on the tariff walls erected against African manufactures, then he would begin to rescue Africa from treading water.

For the African economic malaise is predicated upon how value and price are determined on a "world market" that was established long before Africa had a voice in world affairs. Too often, people parrot the notion that Africa only "accounts for less than 3 per cent of world trade." But they forget that until Opec forcibly revised the price of oil upwards in 1967 and 1973, the alleged contribution of the oil-producing countries to world trade was calculated to be equally derisory.

So Obama and his Secretary of State have to unlearn a lot of the stuff about African development that has become State Department orthodoxy, if he is to be remembered as someone who "did something" for Africa before he left office.

Otherwise, he will just be a tease for the continent; a chimera whose presence in the white House points at great possibilities but delivers exactly nothing.

The author is a Ghanaian writer