Given today's technological advances which have both made the world smaller and also increased military might for even the smallest nations, it is no longer possible for a nation to "bolt its doors" and keep out foreign trouble makers.
[Island countries] A great many islands are pluralistic societies. Some are calm, some have continuing fighting factions, some have been repeatedly invaded. Although their histories are very different, major European islands that can be cited are the UK, Ireland, Greenland and Iceland in the Atlantic; and Sicily and Cyprus in the Mediterranean. Islands have traditionally been battlegrounds for rival sea powers, or for maritime invaders versus natives, because of ease of access by sea. During World War II, the Pacific theatre came to be a predominantly island battle ground. Disputed sovereignty exists or has existed for many islands such as the Falkland Isles (Malvinas) and the Kuril, and argument extends to the Antarctic, which is an entire continent.