EU in twenty-first century, does crisis mean opportunity?Ramiro Troitino, David; Kerikmäe, Tanel; Martin de la Guardia, Ricardo; Perez Sanchez, Guillermo A.The EU in the 21st century : challenges and opportunities for the European integration process2020 / p. 3-9https://doi.org/10.1007/978-3-030-38399-2_1