The empire was different. The excuse is exhausted.

When the conversation turns to colonialism, a particular sentence tends to appear, usually with a sigh of historical patience: but every civilisation has conquered others. The Persians did it. The Romans did it. The Mongols did it. The Ottomans did it. Why single out Europe? The sentence is meant to close the discussion. It should open it.

1. Scale

The Achaemenid empire at its height covered roughly 5.5 million square kilometres. Rome at its peak: about 5 million. The Mongol empire — the largest contiguous land empire in history — reached approximately 24 million. The British empire of 1920 governed 35.5 million square kilometres on every inhabited continent, and the European colonial system as a whole, at one point or another, claimed sovereignty over roughly 84% of the earth's land surface. No previous empire was planetary. This one was.

2. Race as a permanent legal category

The Persian, Roman and Mongol orders absorbed the conquered. A Greek could become a Roman senator; a Christian could rise in the Ottoman administration; the Mongols ruled China through Chinese officials. These empires were violent and extractive, but they did not invent a biological caste that travelled with you for life, was inherited by your children, and remained legally enforceable in the metropole as well as the colony. The European project did. Race, in the modern sense — a fixed, heritable, subhuman status used to organise labour, property, and citizenship — is a colonial invention, refined in the Atlantic system and exported worldwide.

3. Chattel slavery on an industrial scale

Slavery existed in many earlier societies. It was usually a punishment, a war consequence, or a debt status, and it was almost never hereditary in perpetuity for an entire defined population. The transatlantic slave trade did something new: it forcibly deported roughly 12.5 million people across an ocean, stripped them of any legal personhood for life, declared the same condition heritable for their children and their children's children, and built the financial, insurance, shipbuilding and banking sectors of half of Europe and North America on the cash flow. The Code Noir, the Atlantic plantation, and the cotton-finance complex have no real precedent in earlier empires.

4. Capitalism made it a permanent engine

Ancient conquest mostly took tribute and moved on. Colonial conquest restructured the conquered country's economy to serve the conqueror's, indefinitely. Indian textile production was deliberately strangled so Manchester could sell cloth back to India. Congolese rubber, Caribbean sugar, West African cocoa, Bolivian silver, Iranian oil, Indonesian spices — entire continents were reorganised into single-commodity suppliers for European industries. When the formal flags came down, the trade structure stayed. That is why the wealth never went home with the soldiers.

5. It is, in living memory, ongoing

The Persian empire collapsed in 330 BCE. Rome in the West fell in 476 CE. The Mongol khanates fragmented in the 14th century. Algeria became independent in 1962. Angola in 1975. Zimbabwe in 1980. Namibia in 1990. South African apartheid was repealed in 1994. The Chagossians were expelled from their islands by Britain in 1973 and have not been allowed home. France still uses the CFA franc to manage the monetary policy of fourteen African countries. The empire is not ancient history. It is your grandparents' lifetime, and in many cases your own.

6. They knew it was wrong at the time

One of the favourite escape hatches is the phrase "by the standards of their time." By whose standards? Bartolomé de las Casas was writing against the destruction of the Indies in 1542. Equiano was publishing in 1789. The Haitian revolutionaries declared, in 1804, that no human being could be property. Edmund Dene Morel was documenting the Congo atrocities in real time, in English, for a British readership. The Quakers, the abolitionists, the colonised themselves — they knew, they said so, and they were ignored, jailed, or killed. The "standards of the time" included loud objections. The colonisers chose not to listen. That is a moral choice, not a historical inevitability.

7. The wealth is still here

The Roman aqueducts are ruins. The Persian apadana is an archaeological site. The Mongol postal network is a paragraph in a textbook. The wealth from colonialism is a living balance sheet. It is in the endowments of British and American universities built on slave money. It is in the Lloyds insurance market that insured the slave ships. It is in the museums that still hold the Benin bronzes, the Parthenon marbles, and ten thousand other objects. It is in the family trusts of descendants of plantation owners and merchant houses. It is in sovereign debts owed by the formerly colonised to the institutions of the formerly colonising. You cannot say "that was a long time ago" while still living off the dividend.

8. The justification still circulates

Caesar did not write op-eds for The Times defending the conquest of Gaul as a "burden we reluctantly took up to civilise the natives." Niall Ferguson does. Roman senators did not give TED talks on why Carthage's destruction was, on balance, good for global development. Contemporary European politicians do, about Africa, about the Middle East, about the Indian subcontinent. As long as the alibi is still being recited in the present tense, the crime is also in the present tense.