Blue balloons with the slogan "Europa (Europe)" fly during an EU event in front of the Brandenburg Gate in Berlin, one day before the enlargement of the EU, 30 April 2004

Video. European Union marks 20 years since 'Big Bang' enlargement

One senior analyst said the bloc has prospered overall, but there have been ''bumps on the road, otherwise known as Poland and Hungary and possibly Slovakia''. He warned of the possibility several current EU-hopefuls might also violate the bloc's common values and interests.