was the Boer War a turning point in British Imperialism?

Answer 1

no, the Empire was in already in decline . The hype surrounding what was a land and resource grab in behalf of the New World Order, was more a sign of its relative decline. Something like the hype around the Reagan's invasion of Grenada, although the Boer was a disgracefully civilianized war in which the Brits used concentration camps etc.
It may have been the first indication of the already well established relative decline, which was by then happening since the unification of Germany under Bismarck in the 1870s

Answer 2

Hmmm... it may have been when the British really started questioning 1) their invincibility and 2) the moral justification of their "civilizing" imperialism.

In light of 1) screw-ups like the Jameson Raid and 2) the initiation of concentration camps -- for white people, yet.

Sure, the Brits had lost battles before -- in Afghanistan and to the Zulus, for example. But the Boer War dragged on, and on, and on... and is I recall, the peace was negotiated, not dictated.

Answer 3

Not really the Boers lost, but many under Smutts volunteered to fight for the British in WW1 against the Germans.

Answer 4

No, that was the Revolutionary War.