Novelette
Delenda Est
- by Poul Anderson
- Magazine of Fantasy and Science Fiction, December 1955
Events are the result of a complex. There are no single causes. That’s why it’s so hard to change history. If I went back to, say, the Middle Ages, and shot one of FDR’s Dutch forebears, he’ll still be born in the late nineteenth century—because he and his genes resulted fom the entire world of his ancestors, and there’d have been compensation. But evey so often, a really key event does occur. Some one happening is a nexus of so many world lines that its outcome is decisive for the whole future.