The origin of spam in the Pacific Islands is pretty simple and straight forward. Hawaii, Guam, and the Philippines were important strategic locations for Americans during World War II. Japan mounted an invasion of the Philippines, attacked Hawaii, and planned a full-on assault of Guam before U.S. intervention occurred.
Millions of pounds of spam were shipped to GIs fighting in this conflict, making it a critical component of their diet. In the postwar period, ramen (most commonly in its well-known package Top Ramen) became a hit product of the now rebuilding Japan. In the case of Korea, spam literally was the only food available for a time after the Korean War and many soldiers used the food as a form of currency.
It's quite common to see the ramen and spam paired together in that part of the world, an enduring, and potentially quite fattening, imprint of American culture on the Pacific region. Both were easy to produce and in abundance, with spam being extremely easy to obtain thanks to its military surplus.
Even if its introduction to Pacific Islander culture is less than 100 years old, spam has become a staple product on the islands. Guam has added spam to most items on the McDonald's menu and McDonald's is almost ubiquitous in the daily diet. Grocery stores sell as many as over a dozen variations of spam.
All of this comes with a price. Guam, like other nations of native peoples in the United States, has an extremely high rate of diabetes — approximately one in three. The situation is so dire that the World Health Organization has compiled extensive reports on the situation, proclaiming that "abandoning a traditional diet" has cost a heavy price as introducing regular processed foods has brought about Western degenerative disorders. As if by design, government regulation is much looser in the outer territories of the United States, the Philippines, and Australia and resources are more difficult to ascertain. As a result, health labelling is limited to what is done on the mainland; the many locally produced drinks and brands often have no label at all.