The population of England rose rapidly during the 19th and 20th centuries whereas the populations of Scotland and Wales have shown little increase during the 20th century, with the population of Scotland remaining unchanged since 1951. Ireland for most of its history comprised a population proportionate to its land area (about one third of the total population). However, since the Great Irish Famine, the population of Ireland has fallen to less than one tenth of the population of the British Isles. The famine, which caused a century-long population decline, drastically reduced the Irish population and permanently altered the demographic make-up of the British Isles. On a global scale, this disaster led to the creation of an Irish diaspora that numbers fifteen times the current population of the island.
The population in England declined fast during which centuries? (If the question is unanswerable, say "unanswerable")
unanswerable