It's austria.

Austria is surrounded by bijillions of potential enemies, of COURSE people are going to want to DOW you. Many of those nations are potentially just raising armies to send. You try to assassinate an enemy agent and you're SURPRISED that people are mad at you for it?

Maybe I'm in a bad mood because my patch stopped ETW from booting up, but I seriously think you need to go more than a few years into the campaign.

It's not too big of a surprise when the single unit of cannons attacked your army, it had no idea what your army was. The AI only battled because its ability to retreat is dismal; otherwise it would have escaped knowing that you have an army approaching.