other Practical Problems™ the hetalia personfications have to deal with during wartime in my headcanon: figuring out Exactly What Rank on their military uniforms looks plausible when interacting with people not in on the Dirt Children Global Conspiracy. since i’m going with the approach that their existence is kind of hushed up to the general public for all sorts of reasons (like not wanting to make them a target for enemies). so, they may be centuries old and have fought in every single damn war since the collapse of the western roman empire and therefore be experienced like noone ever alive but hey! Random Suspicious Commissioned Officer is going to have a hard time believing some twentyish or thirtyish year old looking fuck isn’t playing dress-up with the rank of lieutenant general.
and then you’ve got nations who have a goddamn immortal and eternal baby face and who struggle to make their visage even look twenty-something in the first place and not like fresh out of liceo. Which actually gives some great comedic moments.
I just have to imagine 19th century Gilbert talking about the struggle of a believable military rank to Feliciano and he just stares at him and says “dude…people usually ask me where my mom is”