As a dual citizen from Europe and a third world country, could I just?
You continue to be a citizen regardless of whether or not you have a passport. For most countries, this isnt a problem. If you dont wish to take advantage of your other citizenship, it doesnt harm you in any way. You can basically forget about it. There are some exceptions: The US and Eritrea tax citizens living abroad. As far as I know this is something you can ignore if you never plan to return to those countries - they wont go out trying to find you - but Im not 100% certain. Its safer to renounce your citizenship as soon as you can if you hold one of those. Other countries have mandatory military service for citizens. You should know if your other citizenship has mandatory military service, and if it does, check into the details. Note that your citizenship can be passed on to your children, and in some cases they may be detained and forced to do military service if they ever visit the country of their other citizenship, even if they didnt know they were citizens. Aside from those two complications, I know of no reason you need to care about your other citizenship if youve already got an EU citizenship.