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.