Pokemon, what happened to you?

[Vipershark]

Gen 2 is definitely a sequel to Gen 1. It happens 10(?) years after Gen 1 does.

as for Gen 3 and Gen 4, there is no indication that they are direct sequels.

According to a few posts back, Gen 4 is happening at the same time as Gen 2, but there is no official word on it.

all that's known is that Gen 2 is officially a Gen 1 sequel in the same timeline.