The constituent countries within the UK used to be independent of each other.
Wales was conquered by England, but Scotland entered into a union voluntarily-ish (I don’t know the full story of the reasons for it; seem to recall something about Scotland being heavily in debt). And the ins/outs of Ireland / Northern Ireland are a whole thing unto themselves.
Also not uncommon for modern countries to have previously been a patchwork of rival kingdoms that later unified—although it’ll vary whether that was by choice or by conquest (with the latter seeming less like a “merger”)
The constituent countries within the UK used to be independent of each other.
Wales was conquered by England, but Scotland entered into a union voluntarily-ish (I don’t know the full story of the reasons for it; seem to recall something about Scotland being heavily in debt). And the ins/outs of Ireland / Northern Ireland are a whole thing unto themselves.
Also not uncommon for modern countries to have previously been a patchwork of rival kingdoms that later unified—although it’ll vary whether that was by choice or by conquest (with the latter seeming less like a “merger”)