So after Henry VII ascends the English throne and ends the Wars of the Roses he immediately begins building up relations with the rest of Europe by marrying his children off: Arthur married Catherine of Aragon and Margaret marries James IV of Scotland.
In our world Arthur died without producing children, which made it easier to marry Catherine to Arthur's brother Henry, who became Henry VIII and we all know how it turned out.
So, instead, what if some way or another Catherine gives birth to a kid but Arthur still ends up dying young? With Henry moved down the line of succession (but still heir to Arthur and Catherine's kid) how will this move things?
In our world Arthur died without producing children, which made it easier to marry Catherine to Arthur's brother Henry, who became Henry VIII and we all know how it turned out.
So, instead, what if some way or another Catherine gives birth to a kid but Arthur still ends up dying young? With Henry moved down the line of succession (but still heir to Arthur and Catherine's kid) how will this move things?