Vice President Joe Biden gave a veritable round-the-world summary of foreign affairs in Cambridge Thursday, but said the United States’ relationship with China is the most essential part of foreign policy.

“President Obama has been direct in public and private with China’s leaders on cyber theft," Biden said. And as the world watches Hong Kong’s young people take to the streets peacefully and demand respect for their own rights, we’ll also never stop standing up for the principles we believe in that are universal — democratic freedoms and human rights.”

Biden spoke at Harvard University's John F. Kennedy School of Government Thursday night. He told a large audience — mostly students — that there are both opportunities and challenges posed by the rapidly changing international environment.

But it was the question-and-answer session with students that brought out Biden’s trademark sense of humor and earnestness.

“You are hardly ever in a circumstance where you choose an ally in an area that shares every one of your values," he said. "But that does not mean we remain silent. You were very polite in introducing me, but sometimes I say controversial things. I don’t think anyone ever doubts I mean what I say. The problem is sometimes I say all that I mean.”

Biden said no American president can ignore human rights in exchange for better international relations, and said nearly every foreign issue has changed in the time he’s been in office.

Biden outlined the Obama administration’s current international challenges, including conflicts between Russia and Ukraine, and Israel and Gaza. But he offered some comfort about the escalating violence in Iraq and Syria from Islamic State extremists.

“We face no existential threat, none to our way of life or our homeland security," he said. "You are twice as likely to be struck by lightning as you are to be affected by a terrorist event in the United States.”

He added that the fight against ISIS will be long, estimating that it could take a "generation or more." But he joked that he’s the White House optimist, bringing the conversation local.

“Never try to improve on Tip O’Neill, who said all politics is local," he said. "But I’m old enough now to be able to improve on it, or attempt to. I believe all politics is personal.”

And he personally greeted students afterward, reminding them that their education makes them responsible for preserving the county’s security, democracy and middle class.