Maybe not the type of answer you're looking for but - Americans stationed in New Zealand often came into conflict with native Māori. For many American soldiers, particularly from the southern states, the site of non-whites drinking in the same bars as whites was discomforting. Fights between Māori and Americans were common. Māori leaders enacted bridge-building initiatives to calm racist sentiments down. Such included inviting Americans to marae, meeting houses, and introducing them to Māori culture.

When I saw this last night, I assumed this question was inspired by Cargo cults, since cargo cults as a metaphor have been bouncing around for the last few years (see cargo cult science coined by Richard Feynman, which appeared in his book Surely You're Joking, Mr. Feynman, cargo cult programming was coined a few decades later), but you didn't explicitly mention them. While so-called Cargo cults predate the Second War World War, the war did a lot to spread throughout Melanesia. More than anything, I think they demonstrate how dramatically lives changed in a short period of time, with the sudden appearance of all this Western "cargo" (and the subsequent withdrawal of most of it again).

The most well established currently is the cult of John Frum on the island of Tanna in Vanuatu (at the time known as the New Hebrides), though there is an interesting rival sect on the same island called the Prince Philip Movement. Smithsonian Magazine has interesting article about John Frum called "In John They Trust", if you'd like to get a little bit more information and description.

Well if we're going to talk about WW2 and it's aftermath, it must be mentioned that some Pacific Islands, including populated ones, were used as nuclear testing sites for the US army, all the way up until the Partial Test-Ban Treaty of 1963 which forbade underwater and atmospheric nuclear tests.

Which ones?

Someone living on Iwo Jima or Okinawa would have an experience quite a bit different than say, Guam, Hawaii or the Solomon Islands.