I know you can stop a trade route by simply stopping soldiers on the road (notice the disapperance of trade wagons). But exactly how does it effect your towns that do get cut off. Moral? Income? and more.

Also do i have a chance to stop the trade routes before.
For example

I notice in my turn that a rebel army has moved upon my trade route. Will my trade be able to continue to trade that turn or has the rebel army stopped in my first turn already. Or does the rebel has to stay there for the duration of one complete turn (theirs) before the Trade comes to a complete halt?

Help needed.