My assumption: Ferdinand III in the years 1636-1639 is an accident or illness, after which it can not have more children. His heirs are the only son of Ferdinand and daughter Mariana, who later became the wife of the King of Spain, Philip IV and Ferdinand died childless in 1654. His father died three years later. Would it be an opportunity to unite all the countries of the Habsburg? And if so, would it be possible inheritance of all the Bourbons after the death of Charles II?