At a crucial moment in the war, Neville Chamberlain – Britain's greatest Prime Minister – resigns?

Impossible as that seems, it could have happened.

In this collection of essays, we look at six ways that the European Great War and the world it made could have gone very differently. From that old standby, "what if Germany had invaded Ireland", to new counterfactuals such as "what if Japan had joined the war", we aim to challenge what we all think we know.

Are our ideas correct or are they wrong? If only another world could tell us…