The development of England as a nation-state occurred because of increasing

Nationalism, is the right answer.

Explanation:

In Britain, nationalism led to the formation of the nation-states.English, Welsh, Scot or Iris were the people who inhabited the British Isles.The formation of the  'United Kingdom of Great Britain' implied that England could impose its influence on Scotland. They could easily suppress the distinctive culture and political institutions of Scotland.The Highlanders of Scotland were banned to speak their own language or to wear the national dress of Scotland. Moreover, a large number of people were forcibly driven out by the English.The Protestants of Ireland established their dominance over a large part of the Catholic country. England successfully suppressed the Catholic revolts against the British government and in the year 1801 Ireland was vigorously consolidated into the United Kingdom.