Romans came from the Italian pensinsula and came to Britain in the early first century. It was a gradual process and they slowly started conquering the different parts of the British isles during that time.
Vikings came from the Northern parts of Europe and they started conquering the British isles in later periods.
Both came and wanted to conquer the lands, while Romans were 'established' conquerors and started governing these areas soon by spreading their culture etc. The Vikings on the other hand had pillaing more in mind and did more of that and did not govern that much from the beginning.
Answer:
The reality of war was in stark contrast to the previous beliefs and attitudes Europeans had.
Explanation:
Pre-war Europe included many nations that celebrated their military. To fight was to be honorable and glorious. However, in the Great War, warfare was much more gruesome than previously. The introduction of gas attacks, trench warfare, and other technological/military "improvements" caused lives to be needlessly lost for little to nothing in advancements. During and after the war, people began to realize that it wasn't worth it and the youth suffered terribly.
I believe it was from May to September 1787, in Philadelphia, Pennsylvania.