"Dutch colonist in South Africa," 1824, from Dutch boer "farmer," from Middle Dutch, cognate with Old English gebur "dweller, farmer, peasant," and thus related to bower, German Bauer, and the final syllable of neighbor; from PIE root *bheue- "to be, exist, grow."
The Boer War (1899-1902), in which Great Britain defeated the South African Republic of Transvaal and Orange Free State, was technically the Second Boer War, there having been a brief preview 1880-1881.