As in the title above, since we read it everywhere about Caruana... why isn't Gata Kamsky considered the first American since Bobby Fischer to fight for the World Championship? He played Karpov in 1997 for the FIDE World Championship.
Kamsky played Anatoly Karpov for the championship during the time after Garry Kasparov and Nigel Short had split from FIDE to form the Professional Chess Association and hold their championship match under its auspices. Thus, the World Championship was "split" at the time - Kasparov held the PCA title and Karpov the FIDE title. In a sense, a split title such as this is no title, so Kamsky misses out on credit for playing for the championship.
This is partly commentary, but hopefully adds a little insight: While my skills are nowhere near good enough to say, it seems that Kasparov is generally seen as the stronger player (vs. Karpov). Thus most people who pay attention probably see Kasparov at the "true" world champion from that time. Between the fact that Kamsky played for the FIDE championship at a time when the title was split and also when the FIDE champion was not the then strongest player, he doesn't get credit for playing for the World Chess Championship.