When did Africans become poor and so unproductive compared to the rest of the world? Was it like this 400 years ago?

Have you by any chance seen one of those before and after images out of Syria?

The point is that one should never assume a static point in history. The past is much different from the present, regression happens.

Think of modern history as being split into three broad phases. The pre-industrial phase (before 1900), the clustered industrial phase (1900–2001), the off-shored industrial phase (2001-TBD). I prefer 1900, because by that time industry had spread across more than just the UK.

In the pre-industrial phase, poverty and productivity measurements aren’t much use. Most humans were poor and a sizeable portion were tied to the soil ranging in freedom from peasants to serfs and slaves. What existed were pockets of prosperity usually in trading/free cities.

At the time, African elites certainly compared and even in some cases surpassed their peers. The coastal trading cities from the Mediterranean down to the Indian ocean were then at their peak.

The turning point was the European discovery of the New World. It created new African elites but with caveats. The rise of the New World dealt two shocks to the earlier period of African prosperity—the Portuguese and later on the Dutch were able to divert the profitable trading routes of the Mediterranean and coastal East African States. The rise of the trans-Atlantic trade incentivised increased warfare, a breakdown in society and the denudation of African labour to the new world. The effects of the above were worsened in the Mediterranean States by recurrent outbreaks of plague.

One era had ended. No part of Africa has yet come close to the parity levels vis-à-vis other powers of that era.

The second era of history saw the rise of the industrial behemoths.

They aggregated knowledge and material., movement of those was restricted by the transportation technology of the era. In that time, however, nearly all African countries lost the space for manoeuvre granted independent States like Japan. The role of foreign technicians in passing on industrial knowledge is often forgotten, from British technicians in the USA and Japan to Germans in Russia. The railway and the telegraph bound the industrial world tighter as Africa was relegated to a source of raw materials. See John Cockerill (company) - Wikipedia, William Thomas Mulvany - Wikipedia for an idea of the spread of industrial ideas.

General peace boosted production but lacking industrial techniques, colonised Africa was getting fast out of step.

Independence came for parts of Africa from the early 50’s but across much of Southern Africa, it would be on hold into the late 70s. All the independent governments sought industrialisation, they went about it in the wrong way. Their markets were too small to afford the import-substitution process which was all the rage, some like Tanzania sought to impose collectivised agriculture. All emphasised a prominent position for the State in the economy that only fostered increased corruption and tyranny. The twin oil shocks wiped out the tottering white elephant ridden attempts at industrialisation.

That led to the 90s, Africa’s lost decade. There were civil wars everywhere and if not civil wars then threats or whisperings of civil war. Robert D Kaplan wrote of The Coming Anarchy and The Economist capped it off with that famous cover.

Time as they say waits for no one. While Africa emerged from the ill-effects of the colonial, feudal, post-colonial and post-feudal hangover, the world kept up a brisk pace. The fall of the wall, the dot-com boom and Steve Job’s return to Apple being the most prominent. However the most pertinent to our times was the off-shoring revolution.

In short, reduced transportation costs and the rise of information technology allowed the splitting off of various industrial processes in other to save costs. Previously the world was divided into lost cost producers toiling in the farms and high-cost industrial nations, now the high-cost industries could merge with low-cost producers for the most impact.

In the $30,000 to $100,000 range … and no this is not a typo.

In fact, if Apple were forced to solely manufacture the iPhone in America, there is a good argument that it would not be able to manufacture any at all.

Glenn Luk's answer to How much would an iPhone cost if Apple were forced to make it in America?

The defining image of the off-shoring revolution

The limitations on personnel movement, advantages of scale and the first-mover principle meant that the off-shoring has tended towards a regional value chain—roughly Germans went to Poland, East Asians went to China, Americans went to Mexico and Canada. If you missed out on integration into the industrial production value chain, that was pretty much it.

The 2000s have seen an improvement as African economies have been buoyed by increased monetary stability and more importantly the commodity cycle triggered by the increased demand for raw materials by the expanding globalised economy.

The challenge modern Africa has to navigate is how to upgrade mass employment from agriculture to industry. The proceeds from the increase in resource demand and the banking, electrical and consumption demands they have fostered have largely accrued to a minority.

The question of whether the transition will be managed successfully, however, is too soon to tell.