I'm not certain the Rhomanian Heartland will ever be threatened again but geography makes her Peripheries too tempting a target.A larger question, I wonder if Rhomania is going to be analogous to the OTL UK and US or to countries like France, Germany, and Russia? The US has not been successfully invaded since the war of 1812. The British haven't been successfully invaded since 1066. France and Germany have lost wars and rebuilt themselves on multiple occasions even into the 1900s.
I am still catching up on the TL but I gather Rhomania was invaded in the last 10 years (1625-35) and crushed its opponents. I wonder if that was the last time or will another power manage to seriously threaten them again?