Land is often used as a tool to define nations. Several different Mesoamerican nations lived in the area we now call the nation of El Salvador before moving on (e.g. Cuzcatlecs, the Lenca and the Maya). The area was conquered and incorporated into the 'Viceroyalty of New Spain'. A viceroyalty is a 'sub-nation' run in the name of a monarch from somewhere else. A foreign sovereign person. It was then part of the Mexican Empire, before that dissolved, and part of the Federal Republic of Central America before that dissolved. In 1841, it became a sovereign state. From 1895-1898 it had a short-lived union with Nicaragua and Honduras called 'The Greater Republic of Central America'. Then that dissolved. In Empires, sovereignty rested in a person and that person wanted more people. To have 'sovereign nations', you have to define a permanent homogenous group of people who want the same thing. Good luck with that. All agreements are temporary.