Why didn't Fievel follow the train tracks after going overboard?
Because he's a little kid and doesn't think things through very well.
Fievel actually does follow them, at first. He later becomes dehydrated and hallucinates his family out in the desert, and he wanders away from the tracks.
Where'd all that food come from?
How do the Native American mice have all that food in the middle of a desert?
There are numerous animals and vegetation that are capable of surviving in the desert, and there are trade routes between those who live out in the desert and those who live closer to oases.
How did they not see it?
How did NONE of the mice realize they were building an enormous, fully functional, and completely undisguised mouse trap?
Maybe they all just never pay attention?
Same reason Cat R. Waul has no trouble tricking them again in quite a few episodes of Fievel's American Tails.
Sparing Tanya
Cat R. Waul was planning to spare Tanya because she's his "diva." Did it ever cross his mind that she might not be that enthusiastic about performing after witnessing him murder her entire family?
He probably didn't count on her finding out.
How is dude still prejudiced?
Something that's always annoyed me: Fievel's dad in the second film telling him to effectively forget about Tiger because "he's still a cat." But then when they get to Green River, he instantly just accepts cats can be good too? Why?
They weren't under the impression that the cats in Green River were good until after they got there, right?
The villain used a puppet to pitch the idea of cats and mice in Green River getting along. Admittedly the father's line there (now that I really think about it) comes later on in the film. But that doesn't quite explain why they weren't too bothered about uprooting for a promised land, again.
Again, Truth in Television: Plenty of immigrants actually did head west because, again, they were told there was opportunity there. It was actually a bit closer to truthful, since even if they would still face social stigmas for being Irish/Jewish/Polish/whatnot, there was a semi-decent chance to make enough money or be invaluable enough that the social stigma didn't matter.
Sing some more, so we get dessert!
Wait, those humans throwing tomatoes and eggs could hear Tanya singing?
I think those were other mice, actually.
No, you can see human silouhettes in the windows opposite. Plus, mice throwing full-sized tomatoes raises questions too =P
Using slingshots
During the final shootout scene, why didn't the cats use guns instead of slingshots?
The one gun that is used is made for a human, so serves more like a large cannon to the cats and mice. One can assume in the An American Tail universe no one has made smaller guns for cats and mice to wield, despite Fievel’s dream sequence at the beginning.
How'd they not notice that?
Is with the humans of Green River not have noticed the shootout between cats mice and one dog?
How'd he get there?
How did Tiger make it out west? It's well established how Fievel's family got there. They took a train that went across the country. There's even a scene showing their journey on a map of the United States. However, Tiger's journey is a confusing mess. He starts out trying to get on the train, runs into a dog, ends up on the front of a train going the opposite direction, then ends up in the river, where he's eventually picked up by a fishing boat. Assuming this somehow gets him to the Mississippi river, he then ends up being dragged by a stagecoach, which somehow takes him another 800-1000 miles, and at roughly the same speed as the train, seeing as he passes by Fievel in the desert later on. Even accounting for cartoon physics, this makes no sense.
