Answer:
Among the advantages we can name the fact that across most Europe there are fertile soils, long river systems, the terrain makes traveling easy and therefore more open to trade since there are no physical borders.
However, this same factor turns into a serious disadvantage in times of war. The lack of physical borders makes countries easier to invade, as was probed in the numerous cities captured by the Nazi regime in WWII. Disease transmissions and undesired immigration are also a frequent problem with open borders.