"Both the United States and the European Union are at a historic crossroads and are facing huge challenges that have one thing in common: the concerns of citizens on both sides of the Atlantic," European Commissioner for Migration, Home Affairs and Citizenship Dimitris Avramopoulos said on Saturday.

The Commissioner was addressing the 2nd International Conference on "Europe in Discourse: Agendas of Reform" held at the Hellenic-American College, the Athens campus of the Hellenic American University.

He also underlined the need for Europe to preserve its momentum and remain united going forward: "Most of the challenges we face today are shared and know no borders. Only working together can we protect and secure the interests of our countries and our citizens. The future of Europe arises from its past and its history, which has proved that the only way forward is a united European Union," he said.

Avramopoulos referred to the close cooperation with the US to deepen cooperation on security and said he was even more confident following the meeting between European Commission President Jean-Claude Juncker and US President Donald Trump "that ended the trade war before it began".

He also referred to the "seismic" crisis facing the EU, 60 years after its foundation, as it reeled from the repeated shocks of the economic crisis, migration and multiple terrorist attacks, noting that Europe, the EU and the member-states had been unprepared for these simultaneous crises.

This had caused some to question the fundamental principles upon which the European Community was founded, when it had emerged from the ashes of two world wars 60 years earlier, he said.

"Dangerous forces of populism and nationalism are weakening the content of Europe and casting the European venture into doubt," he noted, while some government were deliberately feeding euroskepticism and introducing populism into their daily political discourse, turning their backs on fundamental European values, such as the rule of law, solidarity and shared responsibility.

"This phenomenon is the result of the greatest crisis that Europe is going through today: an existential crisis," he added.

According to Avramopoulos, the way that Europe decided to handle the migration and security crises would to a great extent also decide the Union's future.

"In migration we have made progress but more needs to be done...Europe must be better prepared for the next future crisis," he said, while he also referred to the need to defend and protect the Schengen Treaty, calling it the most tangible example of European integration.

"We are the most privileged generation in the history of humanity. We are the only ones who have not lived through war...we cannot allow a return to these dark times," he noted.