The early civilisations of the Americas were limited by its geography – in only two areas did urban revolution occur and civilisations develop: in parts of Mesoamerica, and in the Central Andes.

Hominids first evolved in Africa about 2.5 million years ago. Modern humans first evolved there about 200,000 years ago. But they may not have reached the Americas until as recently as 15,000 years ago.

Africa is the oldest continent, America the newest. Yet, the civilisations of sub-Saharan Africa and the Americas share key characteristics that set them apart from those of Eurasia. Both were constrained in similar ways by geographical barriers.

Africa runs north-south through a series of climatic zones which impede movement and cultural diffusion. Its natural supply of both animal and plant domesticates is relatively poor.

The Americas run north-south for almost 10,000 miles through the entire range of climatic zones. Because of this, what works in one part of the Americas often does not work in others. Different ecosystems require different subsistence strategies, so the value of cultural exchange between climatic zones is less than its value within a climatic zone.

The Americas were well-endowed with plant staples – such as maize, potatoes, squash, beans, and manioc – but not with animal domesticates. Eurasia was home to the wild progenitors of cattle, sheep, goats, pigs, hens, oxen, horses, mules, donkeys, and camels. These provided meat, milk, wool, leather, traction, and transport. The Americas, by contrast, had only the llama, the turkey, and the guinea-pig.

In one respect, Africa and the Americas were different. Africa is not cut off from Eurasia, and African civilisation developed under the influence of Egyptian, Roman, and Arab traders. Crucially, Africa received cattle and iron from Eurasia, and its own production of metals and other commodities was substantially a response to external demand.

The Americas received no such cultural endowment. They were cut off from the global sharing of knowledge and techniques that is responsible for most advances in labour productivity. Consequently, the Americans had no wheel, no iron, and no plough.

These limitations prevented the development of civilisation in North America. When the Europeans arrived, most North Americans were still either Upper Palaeolithic hunter-gatherers or Early Neolithic hoe-cultivators.

In only two parts of the Americas did an urban revolution occur and civilisations develop: in parts of Mesoamerica (Central and Southern Mexico and Guatemala), and in the Central Andes (Peru).

The fact that American civilisation developed entirely independently of Eurasia is the ultimate proof of the common biological identity of humanity: all ‘races’ are equally capable of cultural creativity.

On the other hand, American civilisation faced severe limitations. Its technology was Stone Age. Gold, silver, and copper were used only for ornaments. Its agricultural method was Early Neolithic slash-and-burn.

Because productivity was low and the surplus small, American civilisations tended to be exceptionally brutal. Successful accumulation required extreme forms of exploitation and violence.

The Maya civilisation of Southern Mexico and Guatemala lasted from c. 300 BCE to 900 CE. It was divided into rival city-states under hereditary dynasties of kings who identified themselves with deities.

The Maya built monumental ceremonial centres consisting of plazas surrounded by stone-built pyramids crowned with palaces, temples, and altars. A true urban revolution occurred in the Classic Maya period (c. 300-800 CE), when ceremonial centres like Tikal swelled into jungle cities of up to 50,000 people.

Architecture, sculpture, and painting were developed. Obsidian and jade were worked into objects of quality. Writing, astronomical observation, and calendrical calculation were advanced.

But religion and ideology drove these cultural achievements. They were at the service of militaristic god-kings and a theocratic ruling-class. Wars were fought in part to obtain captives to sacrifice to Maya gods. Art depicts victims being tortured before Maya lords.

Despite intensive agriculture, including the cultivation on raised fields of maize, beans, squash, chilli peppers, and root crops, Maya technique remained primitive. Without ploughs or animal fertiliser, soil exhaustion must have been a perennial problem.

Against the odds, an Early Neolithic economy had given rise to an urban revolution and a network of royal city-states. But the Maya kings and priests were totally parasitic, creaming off precious surplus and wasting it on war, pyramids, and mystical hocus-pocus.

The great debate about why Maya civilisation collapsed somewhat misses the point. What is truly extraordinary is that it arose in the first place, and then that it was able to sustain itself for so long – before collapsing under its own weight.

Waves of barbarian invaders from the north entered the geopolitical space left by Maya decline. The Toltecs eventually established dominance in Central Mexico from c. 950-1170 CE. There was then a further period of fragmentation and warfare.

The Aztec civilisation which emerged from the chaos carried the preceding period’s hallmarks. It was the most hideous product of the limitations and poverty of American civilisation.

The Aztecs founded their capital and ceremonial centre at Tenochtitl√°n in 1345 CE. Between 1428 and 1519 CE, they built an extensive Central Mexican empire. The Aztec state was a centralised autocracy, with a warrior and high-priestly ruling class, and a large professional army.

There was no attempt to assimilate subject-peoples or develop productive technique. Tribute – gold, cotton, turquoise, feathers, incense, and vast quantities of food – were sent to Tenochtitl√°n.

Huge numbers of war-captives were also transported there for sacrifice to the Aztec Sun-god. During one four-day ceremony, 20,000 were murdered at the Great Temple, their hearts torn out as an offering to the Sun, their bodies tipped down the steps.

The Aztec Empire was a crude military imperialism. Its brutality and futility express in an extreme form the limitations of an urban revolution based on Early Neolithic technique. The rate of exploitation, and the terrorism necessary to maintain it, is proportional to the inadequacy of the available surplus. The violence of the Aztec state and the poverty of its subject-people are two aspects of a single contradiction.

The Inca Empire of Peru began to expand in 1197 CE, some two centuries before the Aztec Empire of Central Mexico. But it achieved its greatest extent at the same time – in 1493-1525 CE – and shared some of the Aztec Empire’s essential characteristics.

The Inca state was a centralised military autocracy, with a large professional army, and an administrative bureaucracy which attempted to control the daily life of every subject. At the heart of the empire were great monumental complexes, like the capital at Cuzco, the fortress guarding it at Sacsahuaman, and the ceremonial centre at Machu Picchu.

The Incas controlled an area some 2,000 miles long and 200 miles wide comprising a mix of coastal plain, high mountain, and thick forest. They created an infrastructure of roads totalling an estimated 40,000km, including numerous tunnels, bridges, and causeways, with official rest-houses at intervals of a day’s journey.

Both the Aztec and Inca Empires were anomalous. In Central Mexico and the Peruvian Andes, ancient empires, with their ruling elites, professional armies, and monumental complexes, were constructed on a Stone Age economic base.

The result was exceptional levels of exploitation and violence. The prodigious waste expenditure of the ruling class required ruthless surplus extraction. Imperial rule therefore depended on terror.

Aztec and Inca rulers were hated by their subject-peoples. Rebellion was endemic. When the Spanish arrived in the early 16th century, the Aztec and Inca imperial states shattered like panes of glass: there was nothing behind them, for the common people either welcomed their defeat or participated actively in the struggle to bring them down.