Is there any connection between the Gundam series? I have watched a few (very few) gundam series, and to me they seem like independent mecha anime series.

Is there any connection between the Gundam series? Or are each of them in separate universes?
you have many gundam series with connections!
For example, Gundam 79, the first one, is in the same chronology line with Z, ZZ, stardust memory and others. this series are differents, but in the same line, in the same conflict (AEUG vs Zeon)

But, Gundam Wing, Seed, build Fighters...are differents.

You can follow this example: