US President Barack Obama urged young people to reject cynics telling them they cannot change the world as he held a town hall-style meeting in London.
On the second full day of his visit, Mr Obama addressed young people in Westminster and took questions from them.
He praised the close relationship between the US and the UK, which he said had improved dramatically since the British "burned down my house" - a reference to the torching of the White House in the war of 1812-1814.
The president insisted now was the best time in human history to be alive as he urged the audience to ignore cynical voices saying that nothing could change.
"Take a longer, more optimistic view of history," Mr Obama said.
Asked about his biggest achievement in the past eight years as president, Mr Obama cited bringing in health insurance and dealing with the financial crash.
"Saving the world economy from a great depression, that was pretty good. I'll look at the scorecard at the end. I think I have been true to myself," he added.
Though he did not refer directly to his controversial remarks that a post-Brexit Britain would be at the "back of the queue" when it came to American trade deals, Mr Obama said that generally such economic agreements were difficult due to "parochial" interests and "factions" within countries.
Mr Obama said racial tensions in America still needed to be dealt with and people could not be complacent just because an African-American was in the White House.
"One of the dangers is that by electing a black president people say there must be no problem at all."
Asked about which grassroots movements have been most impressive, Mr Obama cited the marriage equality campaign.
"It's probably been the fastest set of changes in terms of a social movement that I've seen," he added.
The president said he started out backing civil partnerships but gay friends helped persuade him that did not go far enough and full marriage equality was needed.
Mr Obama was urged to do more for the trans community by someone who said they were doing something "crazy" and coming out to him as a non-binary person at the meeting.
Mr Obama joked: "That wasn't that crazy, I thought you were going to ask to come up here and dance with me."
The president then went on to praise the move to equality and said that controversial laws passed in North Carolina and Mississippi regarding trans people using public toilets were state issues.
Mr Obama praised Prime Minister David Cameron for being "ahead of the curve" on LGBT rights issues.
A Sikh questioner called for movement on issues like discrimination at airport security. Mr Obama insisted it was explicit US policy not to racially profile at airports.
The president also praised the Black Lives Matter movement for raising awareness but cautioned you "can't just keep on yelling" at people who want to sit down and talk.
"Seek out people who don't agree with you. That will teach you to compromise. Compromise does not mean surrendering what you believe."
Asked about the peace process in Northern Ireland, Mr Obama said it was an example of what can be achieved when the US and Britain work together.
The president is also meeting Labour leader Jeremy Corbyn following days of uncertainty regarding the event.
News of the meeting with Mr Corbyn, who opposes British military intervention in Syria, came after Mr Obama said the US and Britain were ready to take action to stop the Islamic State terror group securing a stronghold in Libya from which to launch attacks on Europe or America.
Mr Obama said the greatest allies in the fight against terrorism were Muslim Americans.
"If we engage in Islamophobia we are not only betraying what is essential to us, but, just as a practical matter, we are engaging in self-defeating behaviour if we are serious about terrorism."
Though billed as an opportunity for young people to connect with Mr Obama, there were also some famous faces in the audience including Annie Lennox, Benedict Cumberbatch, Holly Valance, Bank of England governor Mark Carney and designer Ozwald Boateng.
After meeting the Labour leader, the president joined Mr Cameron to play golf at The Grove, Chandlers Cross, Herts.