Often your issue is pretty much the opposite of what you might expect. Older houses were built with an expectation that there would be airflow, and usually with lime plaster walls that are breathable (and lath and plaster ceilings that insulate relatively well - heat and sound), and often without cavity walls (so single skin) etc.. So they act differently from later construction. A lot of the time that plaster ends up either being replaced by gypsum, being skimmed with gypsum, or being wallpapered/painted with materials that aren't breathable, and people block off the various ways you used to have airflow..

When people insulate, especially if they do it relatively cheaply/simply add insulating material to cut air flow, you end up in a situation where you don't lose heat, but you do retain moisture and you end up with condensation. The result is then really commonly wet wall areas (spots if you have bits of patched plaster for example, or corners where external walls are cold), and then mould. It can be more of an issue if you have lots of layered crap on the walls (think multiple layers of wallpaper and then paint...), especially if you also end up with damp between layers...

That said, if you are stripping the wallpaper (and good luck with that if it hasn't been done in a while, I think the record we had was two dozen layers...) take a look at what is behind it. You should be able to spot lime plaster (it'll look more like concrete), if that's what you've got, and its in good condition, then let it dry out before you do anything else. If it does dry out nicely then you are on to a winner and I'd suggest taking a look at the wallpaper you use, some are permeable/breathable, some are not, you'll likely want something more permeable.. If however you can't dry the room out (without using a dehumidifier...) when you have the wallpaper off, you'll probably want to talk to someone about balancing insulation with airflow, if that's even possible.

Although if its a rental, speak to your landlord first..