R. D. Laing

An independent state does not pay too dear a price for its independence in accepting the sufferings of war when it cannot avoid them; a state which has lost its independence may find at least some compensation in the fact that its protector procures for it peace with its neighbours.

The historical novelist has to consider what has actually happened, while the SF writer is dealing in possibilities, but they are both in the business of imagining a world unlike our own and yet connected to it.