That's pretty scary. Don't you have employee protection laws in the States? Surely you can't sack someone and not give a reason.
In most states, you can be released without cause.
The only protections are for provable abuse or discrimination.
If someone fires you because they "don't need you anymore", it is up to you to prove that they were discriminatory in doing so.
In Oregon and Washington, it is almost impossible to win a case against an employer, unless there is clear cut evidence to the contrary.
If this case were tried in either of those states, it may be winnable--IF they hired someone to replace your exact route.
If they divided up your route amongst the remaining drivers for a time, you wouldn't win--even if they subsequently decided that they "did" need your job, and rehired for the position at a later date.
Either way, you'd probably have a very difficult time finding a lawyer to take the case because they will probably only do so with a guaranteed payment, win or lose.