Original: Originally the bulk of the independent Boer South African Republic , after the Anglo-Boer War of 1899-1902 it became the Transvaal Colony , and one of the founding provinces of the Union of South Africa , with its regional capital in Pretoria , from 1910 until 1994 .
Simplified: It is one of the original provinces of the Union of South Africa from 1910 until 1994 with capital in Pretoria .