Astronomy history is fascinating to me. We used to think that other galaxies were just nebula in the milky way.

We would still have all the stars from our own galaxy to study, but I think that given how much we have improved telescopes with the intent on studying CLOSE stars, those improvements would have led to the discovery of galaxies 100 million LY+ away.

Fun fact: we don't know what's on the other side of the galactic disc from us. As we look toward Sag A*, the supermassive black hole at the center of the galaxy, there's too much dust and non-luminous matter in the way, and we can't really see what's past a certain point. There's also something pulling all the galaxies around us (and us) toward it, in that big patch of what we can't see. It's called the Great Attractor. We know it's pulling on us because of red/blue shift of surrounding galaxies, but we don't actually know what it is that's pulling. It COULD be a large cluster of galaxies whose gravity is just pulling us all together, but it might also be some cosmic eldritch horror that's literally consuming the universe. That last one is slightly less likely though...