R.A.F. MILDENHALL, England — President Biden began his first overseas trip by telling American troops in Britain that the future of the world depends on restoring the longstanding alliances with European countries that have been “hardened in the fire of war” and built by “generations of Americans.”
Speaking to troops at R.A.F. Mildenhall, he called his weeklong diplomatic overture “essential,” saying that no nation acting alone can meet the world’s challenges. But he also vowed to stand up to adversaries like China and Russia, pledging to tell President Vladimir V. Putin of Russia “what I want him to know.”
On the eve of meeting with European leaders rattled by Russia’s aggressive movement of troops along Ukraine’s borders, Mr. Biden pledged to “respond in a robust and meaningful way” to what he called “harmful activities” conducted by Mr. Putin.
Mr. Biden also cast his trip in broader terms, as an effort to rally the United States and its allies in an existential battle between democracy and autocracy.
“I believe we’re in an inflection point in world history,” Mr. Biden said, “a moment where it falls to us to prove that democracies not just endure, but they will excel as we rise to seize enormous opportunities in the new age.”
