As expected, my troops can move into territory that:
- Belongs to me
- Is occupied by me
- Belongs to a nation that grants me military access
- Belongs to a nation I am at war with
However, in some cases I have noticed that my armies can walk over foreign territory when I have no diplomatic relation with the owner. For instance as France, if I fight wars with Denmark or Southern Italy, I am sometimes able to walk my troops all the way through 5 or so different nations, most of them neither allied with me nor otherwise granting access rights. This usually creates a "you have troops in foreign territory" message in the top left.
I also notice that sometimes foreign armies walk over my territory, even though again I have no relation with them and never gave them access. For instance, right around 1444 as Spain, sometimes Genoa will just waltz right through Spain.
Why are armies sometimes able to enter foreign territory without access rights? What is the full of list of conditions that allow a troop to enter a given territory?