Basically: In some countries, the pledge is with the constitution or the people, but in others (like constitutional monarchies), its a pledge to the (constitutional) monarch and their successors.
What is your opinion on this loyalty pledge? Do you believe it’s a reasonable request?
(For context: My mother and older brother had to do the pledge to gain [US] citizenship so the idea of deportation isn’t looming over our heads. I didn’t have do it because I was under 18 and my mother’s citizenship status automatically carried over to me according to the law.)
You’d need more war to solve that. In Europe, borders usually run along a natural defensible lines, like rivers and mountains.
Or battle lines: Belgium netherlands