okay, so what the european union does is it somehow establishes this control over european countres (with exeptions) and a few non-european ones (french guiana if i'm ot mistaken)... through being part of the european union, one gets economic advantages when it comes to trade of product etc...
a country also benefits from establishing good relations with other countries etc...
thing about those who do not wish to join may be because they do not want to take part in this system... getting in the EU groups entails responsibilities to help your co-EU countries etc... maybe those countries who do not wish to join thinks that they are better of alone etc,...
another factor is, EU sometimes rejects membership of a country due to very poor conditions... in such a way that it is very dificult and risky to invest in that country
anyway, all in all EU promotes comraderie and mutual development among its member countries..

as for the political stuff, it's your turn to research

great day!
