Keith Roberts’ 1968 Pavane is a collection of linked alternate-history stories.
Mortally wounded by an assassin’s bullet, Queen Elizabeth dies. The ensuing Protestant/Catholic civil war leaves England vulnerable to external enemies. England is conquered, its armies used to crush the rest of Protestantism. The Catholic Church reclaims its role as the sole religion of Europe well into the 20th Century1.
I can’t see a way of discussing the background without massive spoilers so here, have a massive spoiler warning.