It's how the battles are resolved. They are done one by one, not at the same time. Therefore, Niklas was able to attack Lig with his Infantry, they won, meaning the path was clear for the cavalry to reach the next battle, Ten. If they did not attack Lig too then the cavalry would have been stopped.
Please Note: There are some minor adjustments to the rules.
1. Water tiles now count as one tile for Airships, but they may only cross one sea tile per flight. This would mean that, for eg, an Airship in Eas could go NoS -> Nor -> Rhe and drop infantry at Rhe.
2. From now on, if a player attacks a fort or city that have units hidden inside, and the defending player wins, the defender's remaining units will not be shown on the map. I will tell you how many remain in your gold PM.