https://www.eurofound.europa.eu/sites/default/files/ef_publication/field_ef_document/ef1710en.pdf
https://theconversation.com/crisis-del-regimen-democratico-la-dominacion-de-los-partidos-politicos-en-espana-226276
https://www.ips-journal.eu/topics/european-integration/uniting-europes-distant-family-6734/