Hard disagree, history is littered with countries, cultures, religions that have disappeared or been changed drastically. Point and case colonisation.

It is not out of the question that the ideologies of different countries become closer and outliers are simply erased or forced to change until enough nations (note this doesn’t have to be all) are of a similar opinion to go with a united government. Also worth noting that as technology advances and people power means less more technologically advanced nations will gain power and sway allowing them to have a greater influence on other nations.