Addressing the European Parliament in Strasbourg, French President Emmanuel Macron urged Europeans to halt a retreat into nationalism and rebuild the European Union as a bulwark of liberal democracy.
He won applause from lawmakers after condemning the rise of "illiberal democracies" even within the EU.
Echoing the language of historians about Europe's slide into war a century ago, Macron said he would not belong to another "generation of sleepwalkers" and let the EU wither in what he called an atmosphere of "civil war".
But it was a "game of fools" to halt or reverse sharing sovereignty among EU states in the face of global challenges, ranging from climate change and mass migration to the growing power of multinational corporations and authoritarian states.
"We need a sovereignty that is stronger than just our own, which complements but does not replace it," Macron said in Strasbourg, a French frontier city which has become a symbol of Franco-German reconciliation after centuries as a prize of war.
Many MEPs praised his vision and work, but some still remained sceptical, like Syed Kamall, a Conservative from London.
"Rather than sleepwalking to use your phrase towards your goal, it should be presented to voters across the EU with an honest disclaimer in large letters, bold and underlined, that member states will become less and less sovereign as the EU becomes more and more sovereign as you wish to see."
Macron's speech was closely followed by reporters - some of whom saw his fight for more European integration as an uphill battle.
Enrique Serbeto from the Spanish daily newspaper ABC said that Macron probably realized that he alone - not even with Germany - cannot carry out any reform project.
There are a lot of different sensibilities in Europe.
Macron was speaking at the invitation of the European Parliament, which has asked leaders of all the member states to give their views on the EU's future following Brexit.