In the West, there was a period known as the Agricultural Revolution in which agriculture became more efficient. In particular the smallholder farmers of feudal times were thrown off their land and sent unto the cities to become the urban proletariat whilst those left behind worked as agricultural labourers on farms that had been enclosed into larger fields owned by an aristocratic landlord. This led to the decrease of agriculture as a share of the economy and the rapid increase of the industrial sector of the economy, leading to the Industrial Revolution.
Yet Africa, in spite of its history under European colonialism, remains agriculturally backward. Why is this? Why did the European powers not succeed in creating an agricultural revolution in Africa through the creation of large commercial farms in place of smallholder, subsistence farms? I have read of attempts to improve agriculture by the socialist regimes of Ethiopia and Tanzania during the Cold War which also involved Soviet-style collectivization, with the state playing the same role that the aristocratic landlords of the Agricultural Revolution did in merging small firms together into larger, more efficient ones that employed less workers, but these appear to have failed. Even so, there has been much urbanisation in Africa despite the lack of a wholesale transformation in agriculture as occurred in European countries. I find this to be particularly poignant in Zimbabwe, where, despite the implementation of land reform by the Mugabe government, the underlying problems of primitive agricultural techniques and the dominance of subsistence over commercial farming (the latter of which was carried out by the predominantly white farmers) remain.
I have so many thoughts on this, but so little time. First, the idea that small scale agriculture is by its nature unproductive is false. There is a pretty big literature that shows that for most crops, small farms consistently have higher total factor productivity (that's the productivity after taking land and capital into account) than big commercial farms. In Africa, large white owned commercial farms only survived because of government subsidies of one form or another.
As far as the failure of a green revolution in Africa is concerned , I would point to a couple of features. The green revolution was a series of major advancements focused on the creation of high value rice and wheat seed varieties. This had some major problems for Africa. First, most countries did we're not major growers of either crop. Second, these new high yielding seed varieties were a lot more productive, but a lot more fragile. They needed lots of fertilizer and lots of irrigation to thrive.
Unfortunately, the various governments in Africa were not especially interested in agriculture in the immediate period after Independence. There's some important evidence showing the governments were systematically biased against farmers. These economies collapsed during the 1980s, and IMF sponsored structural adjustment programs ended up slashing what subsidies to farmers remained (this wasn't the goal of structural adjustment, but more of an unanticipated side effect). Governments in Africa rarely invested enough in agricultural extension services, training farmers in new methods, creating seed varieties for local conditions, in creating effective systems to allow farmers to get access to credit, and building irrigation systems. As a result of all of this, farmers in Africa never saw a green revolution that you saw in Asia and Latin America.
But there were important exceptions. Zimbabwe actually saw one first under white rule based off of maize cultivation. However, after the end of white rule, Robert Mugabe government made a major effort to get farmers access to fertilizer which allowed for maize yields to nearly double in a decade on the farms of small scale black farmers. Part of the tragedy of Mugabe is that he did a lot of good before he started doing a lot of bad.
There's a lot more to be said about the modern history of farming in Africa, but that's outside the scope of this subreddit. I can provide sources as soon as I am at a computer and not on my phone in the evening of today.