Chuck Hagel

The glory of the old Irish nation, which in our hour will grow young and strong again. Should we fail, the country will not be worth more than it is now. The sword of famine is less sparing than the bayonet of the soldier.

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.