France's President Emmanuel Macron has called for closer ties between his country and Germany, saying Europe "has the obligation not to let the world slip into chaos".
Mr Macron is in Berlin for the country's annual day of mourning for victims of war.
In a speech to Germany's parliament, he said Europe must not "become a plaything of great powers".
Mr Macron wants a more integrated EU, with a joint eurozone budget.
He also wants Germany's backing for a European Army, which he has said would reduce the bloc's dependence on the US, and a new tax on internet tech giants.
German Chancellor Angela Merkel has expressed tentative support for some of these ideas, but others are controversial in Berlin.
'Our true strength lies in unity'
The French leader spoke of nationalist forces "with no memory", and urged progressive forces to unite in an uncertain world.
"There are too many powers that wish to thwart us, that interfere in our public debates, attack our liberal democracies and are trying to pit us against each other," he said. "And in this global order, which we have to take very seriously, our strength - our true strength - lies in unity."
US President Donald Trump was moved to a Twitter tirade by similar remarks from Mr Macron a week ago, when the French leader called nationalism a "betrayal of patriotism" while commemorating the end of World War One.
The French president acknowledged that unity could be "scary," and would mean nations pooling their funds and decision-making - but then asked: "Is it better to remain locked at a standstill?"
The French and German leaders met for talks after Mr Macron's speech, and were set to discuss migration, defence co-operation and tax structures for digital companies.
France and Germany are expected to unveil plans for a limited joint eurozone budget on Monday.
"You made clear with an impressive speech how important the German-Franco friendship and co-operation is, and what role it plays in the European context," Mrs Merkel told Mr Macron.
"You said we are at a crossroads... and this is exactly what I perceive. Those of us born after the war are responsible for the lessons that we learned."
She intends to serve out her fourth term as chancellor, which ends in 2021, but some commentators believe she may be brought down before that by in-fighting within her party or the broader government coalition she leads.