The eruption of Campi Flegrei in 1942 crippled human civilization for many years, especially in Eurasia. North America was affected to a lesser extent and the Second World War played out differently than in the original timeline.
Eventually, as with so many disasters, things begin to recover. American television develops and begins producing shows to entertain their customers. One such show was a police/espionage show created by Leonard Freeman set in the new state of Hawaii (admitted to the Union in 1963 as the 49th state). The premise of the show was a fictional state police agency in Hawaii. The leader of the agency, Steve McGarrett (played by Jack Lord) also had ties to US Naval Intelligence which brought international espionage plots into this police drama.
It premiered during the 1968-1969 season with an allegedly rogue Japanese secret agent Katsuo Kawaguchi (played by George Takei who played a secondary character on the obscure sci-fi show Star Trek during its second and third seasons). The SP team would combat criminal organizations, enemy agents, serial killers, and drug dealers. A large number of scenes were filmed on location in some of the most beautiful areas of the islands. The locations, varieties of stories, and the hard work of Jack Lord made the series a great success.
When the Chinese War started in 1972 a number of stories dealt with American servicemen stopping at the islands on the way to the front or returning for R&R after a tour. For a few seasons the espionage elements of the series overtook the crime drama. The writers were not afraid of tackling controversial issues such as the anti-war movement, combat fatigue, and even less than altruistic elements of the American government.
After the nuclear attack on Bejing by a European Reich unit attached to the Japanese Empire the ratings of the show began a rapid decline. Americans were turning more to comedies and trying to forget the horrors of war. The series was cancelled after its 9th season (1976-1977).
In 1997 the series was revived for three seasons with a mostly new cast. James MacArthur returned as Dan Williams who was now the Governor of Hawaii. Gary Busey played the new head of the agency. The new series suffered from mediocre writing and lacked a visionary mind behind it to make it as great as the original. The international storylines were weak. The Japanese Empire was becoming more moderate and the imminent independence of Manchuria made the depiction of them as the primary villains of the series a bad idea. The third season focused on an anti-drug message and seemed like too much of a lecture and not very entertaining.
An attempt to reboot the series in 2010 failed. It is bound to happen at some point in the future as interest grows.
After a major change to human history caused by a super-volcano erupting, even a relatively minor eruption, it seems unlikely that television would be the same. However Hawaii would still have been made a state, Leonard Freeman, Jack Lord, and James MacArthur were all born before the disaster and America was not affected as badly as the rest of the world. I've been thinking about how television and movies would be different in alternate timelines. When I determined in this timeline that Alaska would become the 50th state in 1976 - having taken a long time to recover from the volcanic winter, I thought how a popular show like Hawaii Five-0 would have been different since it wouldn't have been Five-0. Hawaii Four-Nine didn't really have the same ring to it.
The successor series I mention in the post is inspired by the pilot of a OTL spin-off pilot that was made in 1997. When I had heard of the recent rebooting of Hawaii Five-0 I the fan of the original series in me had said it should have been set in the same 'universe' as the original, possibly with James MacArthur coming back to play the governor and reactivating the state police..... last night I found out that my lame idea was used back in 1997 for an unsuccessful pilot!
The series title image I have in the post I created using a public domain image and basing it off the iconic one from the real-world show.