This year's elections will no doubt provide plenty of opportunity to attack "colonialism" and "imperialism". The 120th anniversary of the start of one of the worst episodes in the long history of British imperialism is likely to pass unnoticed, however. It was on 11th October 1899 that the Boer War – strictly speaking, the Second Anglo-Boer War – broke out.

Like the Second World War, which broke out 40 years later when Adolf Hitler's armies invaded Poland, it was engineered by one man – Sir Alfred Milner, British high commissioner in South Africa. He was able to manoeuvre his superiors in London – among them the gung-ho colonial secretary, Joseph Chamberlain, and the prime minister, Lord Salisbury – into bringing about his war to crush Paul Kruger's Transvaal republic and so assert British supremacy.

Milner's pretext was the denial by Kruger of franchise rights to the uitlanders in the Transvaal. Here too there are parallels with Hitler. The maltreatment of ethnic Germans in Czechoslovakia was the Nazi leader's pretext for seeking to annex parts of that country. Hitler was furious that the concessions which British Prime Minister Neville Chamberlain (Joseph's son) forced upon the Czechs at Munich enabled him to achieve his objectives short of declaring war. It was not long before he invaded Czechoslovakia anyway.

So also, Milner contemptuously brushed aside all the concessions that Kruger's government – under pressure from Afrikaners in the Cape – was offering. Milner, who met each concession by escalating his demands, was not interested in diplomacy or compromise. "It's our country you want," said Kruger, bitterly and accurately.

"Sir Alfred Milner's war" – as the historian G H L Le May described it – brought 450 000 British troops to South Africa to crush a very much smaller number of armed Boers, who signed peace terms on 31st May 1902 only when they recognised that to keep on fighting would destroy their nation. But the war is most notorious for the deaths of 27 000 Boer women and children in concentration camps, along with some 14 000 blacks (though the black victims are often forgotten).

The camps were established to accommodate families whose farms and homes were burnt by the British when the Boers switched to guerrilla warfare after declining to surrender when the British captured Pretoria. This policy was initiated by the British commander-in-chief, Lord Roberts, and later extended by his successor, Lord Kitchener. It horrified none other than Milner himself, who described it as "barbarous" – a phrase echoed across Europe when the British Liberal opposition leader, Sir Henry Campbell-Bannerman, adopted it to accuse his country's armies of "methods of barbarism".

Not long after becoming prime minister in 1905, Campbell-Bannerman handed the whole of South Africa back to the Boers under a constitution which entrenched white minority rule. This dismayed black leaders, whose protests were ignored in London by Liberals and Conservatives alike. But Jan Smuts, effectively number two in Louis Botha's first South African cabinet, hung Campbell-Bannerman's portrait behind his desk at Doornkloof, his home at Irene outside Pretoria.

This brazenly imperialistic war eventually created deep divisions among the British. But initially it had the support of both Left and Right. The socialist Sidney Webb said it was both "wholly unjust" and "wholly necessary". Another great socialist, George Bernard Shaw, said that a "great power" had to govern in the interests of "civilisation" as a whole instead of leaving the Transvaal goldfields to "small communities of frontiersmen".

Who "won" the war? For all practical purposes, the Union of South Africa founded in 1910 was a sovereign state. But it was also part of the British Empire (later the Commonwealth), as a member of which it twice went to war against Germany. It did so not at the behest of imperialists in London but on the initiative of its own leaders, principally the one-time Boer generals Botha and Smuts. Although they argued that going to war was in South Africa's own interests, they faced bitter opposition, and sometimes armed resistance, from some of their erstwhile followers both times round. But the British could not have hoped for better allies than these two free "frontiersmen".

* John Kane-Berman is a policy fellow at the IRR, a think-tank that promotes political and economic freedom. If you agree with what you have just read then click here or SMS your name to 32823. Each SMS costs R1. Ts and Cs apply.