President Volodymyr Zelensky of Ukraine said at the World Economic Forum on Tuesday that it was time for Europe to stand strong and remain united as the United States installs a new president skeptical of global alliances and continued aid to Ukraine.

“Europe must shape history for itself and its allies,” he said in a speech to dozens of government leaders at the annual Alpine summit in Davos, Switzerland.

Mr. Zelensky spoke less than 24 hours after President Trump was sworn into office for the second time. But already, he said, “most of the world is thinking, what is going to happen to their relationship to America.”

While America remains an “indispensable ally” that can help bring an end to Russia’s war of aggression, Mr. Zelensky warned European leaders that they do not have the luxury of an ocean separating them from the revanchist regime in the Kremlin.

Therefore, he said, Europe must ensure its voice is heard in talks to secure not only a rapid end to the fighting in Ukraine but a just and enduring peace.

“Will President Trump listen to Europe or will he negotiate with Russia and China without Europe?” Mr. Zelensky asked. “Europe needs to learn how to take care of itself.”