Final answer:
Italy and Germany are the two major Western European nations that did not unite until 1869/1870, profoundly changing the European power structure.
Step-by-step explanation:
Which two major Western European nations did not unite until 1869/1870? The correct answer is A) Italy and Germany. These two regions had ancient regional identities and shared histories but lacked political unity prior to the second half of the 19th century. National unification in Italy and Germany was achieved through political and military efforts, profoundly impacting the balance of power in Europe. Italy was last united under the Roman Empire, while Germany had never been truly united in a nation-state structure before this time.