That war, which saw the first concentration camps set up by the British military to keep Boer villagers, mainly women and children, from supporting their own soldiers and guerillas between 1899 and 1902, was widely opposed within left and liberal circles in Britain. There was justified suspicion that a specious pretext had been found for invading the Boer republics, in which the British government, Transvaal mineowners, Cecil Rhodes and others were implicated.
However, the ugly side of 'pro-Boer' agitation was its stress on the involvement of Jewish settlers in South Africa.
As Hirshfield says,
If it could be demonstrated that the British government had been tricked into war by the machinations of shady Jewish capitalists and that the public had been intentionally misled by omnipotent Jewish presslords, then sufficient pressure might indeed be generated to end what its opponents considered an immoral war. That the pursuit of this worthy aim involved an appeal to a base and discreditable prejudice seems to have little troubled the various socialists, radicals and labourites who utilized the shorthand of "Jewish finance" as a convenient means of epitomizing the dark underside of British imperialism.The anti-semitism of Hyndman's Social Democratic Federation and its newspaper Justice has been documented, but Hirshfield also shows that other sections of the left were not immune to what Bebel called 'the socialism of fools'. Keir Hardie's Labour Leader accused Jewish capitalists of engineering war "in order to screw down white wages on the Rand"; and John Burns, whose diaries reveal, sadly, a visceral and physical dislike of Jewish individuals, claimed that the British army had lowered itself to become "the janissary of the Jews".
Perhaps the least divisive, if saddest, moral which could be drawn from this would be that there are good people around who can still be carriers of social toxins; but it's depressing to have to make the point a hundred years on.
London Metropolitan University
See also this speech by Charles Lindburgh for the anti-war movement in the US in 1941.
See also Mearsheimer and Walt.