I don’t know what history book you are reading, but i suggest getting a better one.
Rhodesia unilaterally declared independence from Britain.
http://en.wikipedia.org/wiki/Unilateral_Declaration_of_Independence
Its a bit like you think that if you walk about on your parents you can claim to be abandoned by them....i think you have a certain axe to grind.....
Rhodesians knew Britain was going to turn over the management to blacks (as the did in Uganda & Kenya), so they acted; they certainly never preferred to fight the war alone, but saw that as the only alternative.
I’m not sure why that is hard to understand; there is hardly an axe to grind. Britain did the same thing in their African and Asian colonies, and is attempting to in its Northern Ireland colony (which is no longer an industrial powerhouse, but rather a population on the dole). If more white Brits had moved into other colonies, that scenario would have played out all over.