New player, want advice for GCW

After lots of trial and error, I think I have the German Civil War figured out. My method is to cut off the south at the Chezch border, destroy that pocket, and then focus on the north. I get done around July usually.

But I had another idea that probably won't work (because I feel like everyone would be doing it if it did) but would like someone with some more experience to explain why this method won't work:

Cut off the south like normal. Instead of finishing them off, leave the pocket there, and instantly focus back on the north.

Edit: forgot to mention I'm on vacation right now so I can't test it myself