JMEnglish, I apologize for not responding to your question until now. I’m not sure how I missed it when you first posted it, but I’m just seeing it for the first time now.
I don’t give a lot of emphasis to the Treaty of Westphalia in the course. What mainstream historians will normally say about its significance is that it marks the end of using religion to justify war. Among Western states that’s still true, although in the broader international order? Maybe not so much.
The other thing that’s often said about it is that it establishes the modern nation-state system. I think that’s a more dubious claim.
Could I ask you to be more specific about what Westphalian principles you’re referring to if you have something else in mind?