I have moved to another state, now I can't attack enemy base, why?

Have you migrated to the other state permanently? Or just used an advanced teleport to travel there. If you have not migrated then you can only attack players during an appropriate event, for example a clash of zone kill event, and only if you are at war with that state.

If you have migrated then possibly there is a time out or it may be a a bug. You can try checking with the developers using the in game support option if it seems broken.