Many European countries that we know today didn’t exist in their current form that long ago and had a major war preceding the establishment of that nation. Kingdom of the Netherlands and the Grand Duchy of Luxembourg were formed in 1815 and Kingdom of Belgium 1830 before they were always subjects of a bigger empire or kingdom. Unification of Italy 1871 when Rome was finally captured and French Republic formed in 1792, France’s latest form is the Fifth Republic established in 1958. Germany only unified in 1866 before that time it was a bunch of smaller states and kingdoms, then after 1919 became the Weimar Republic, Federal Republic of Germany in 1949 and then fall of the wall in 1989. Independence of Greece 1821. Those examples aren’t the only ones and don’t forget the western Balkans, those nations were all formed in the 90’s.
It’s not that the country of America will disappear after a civil war but it might not be called the USA anymore.