This paper aims to analyze geopolitical tensions developed in the 21st century, as evolving from disputes between the global powers, and how these dynamics motivated new multilateral reshapings in the European Union (UE). As a general objective, this paper aims at analyzing the causes of the growing nationalism in the EU in the 21st century and its impact to regulate multilateral relations, as reflections of tensions between the global powers United States (US) and China. As specific objectives, the following ones were highlighted: (a) locating elements of identity and nationalism in the relationships between/among EU members; (b) analyzing instances of multilateralism in the relationships between/ among Member-States; and (c) making considerations on the possible impact of tensions between the global powers US and China to motivate the definition of multilateral reshapings. For that, the theoretical foundation addressed the discussion between globalization and globalism; and the democratic legitimacy comprised by the identity-nationalism continuum. And the methodology was designed as bibliographical research on themes identity and nationalism, relevant to the cross-sectional axes legitimacy and populism, and study case with comparative analysis of speeches delivered by Theresa May, on the Brexit proposal, on January 20th 2017, and by Donald Trump, on his inaugurationday, on this same date. As a result, it was found that, within a context of shifting global order, the identity-nationalism continuum was resignified, in the face of the influence of growing populism and democratic legitimacy deficit, to some extent. Therefore, understanding how global tensions motivate this new multilateral reshaping is essential to align new economic and political tendencies, without destabilizing ongoing partnerships and the potential of interaction between/among European States.