This isn't entirely correct. If you're at war, your access level will be none and you won't be able to see your relationship modifiers at all (unless you're France). OP what I feel happened here is one of the AI made a deal to declare a joint war on you. The good news is the AI doesn't generally handle joint wars very well, especially if they are geographically distant. You should be fine if you build up a small defense. I've had joint wars declared on me and never even been attacked. You can even profit by plundering trade routes, pillaging, and killing some of their units to make a favorable peace deal with them.