President Obama urged a “common effort” to ensure life liberty and the pursuit of happiness are made real for every American, during his inaugural address in Washington DC on Monday.
“We recall that what binds this nation together is not the colors of our skin or the tenets of our faith or the origins of our names,” he said.
“What makes us exceptional – what makes us American – is our allegiance to an idea, articulated in a declaration made more than two centuries ago: ‘We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable rights, that among these are Life, Liberty, and the pursuit of Happiness.’”
“Today we continue a never-ending journey, to bridge the meaning of those words with the realities of our time. For history tells us that while these truths may be self-evident, they have never been self-executing; that while freedom is a gift from God, it must be secured by His people here on Earth.
He added: “The patriots of 1776 did not fight to replace the tyranny of a king with the privileges of a few or the rule of a mob."
Stumbling over the words a little, Obama took the oath of office, administered by Chief Justice of the US Supreme Court and watched by a crowd of hundreds of thousands of in the US capital.
Obama is only the 17th president to be sworn in for a second time and is the third two-term president in a row after Bill Clinton and George W Bush.
The president appeared relaxed, chatting to dignitaries including former presidents as he waked out on in front of the US Capitol building.
In the run-up to the ceremony, Obama tweeted: “I'm honored and grateful that we have a chance to finish what we started. Our work begins today. Let's go.”
Obama formally took the oath on Sunday, as by law presidents have to take office on 20 January. However the fact Monday’s event was purely ceremonial did not appear to dampen the sprits of the crowd who cheered wildly and shouted the president’s name as he began his speech.
This year’s inauguration fell on Martin Luther King Day, a public holiday that marks the birthday of the civil rights leader. Obama, the first African-American president, said that through “blood drawn by lash and blood drawn by sword”, the US learned that “no union founded on the principles of liberty and equality could survive half-slave and half-free”.
And Obama used his speech to call for Americans to “move forward together” and urged greater equality for women, gay people and immigrants.
“We do not believe that in this country, freedom is reserved for the lucky, or happiness for the few,” he said.
He added: “Let each of us now embrace, with solemn duty and awesome joy, what is our lasting birthright. With common effort and common purpose, with passion and dedication, let us answer the call of history, and carry into an uncertain future that precious light of freedom.”
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Obama also used his address to insist his administration would attempt to tackle climate change, arguing that ignoring it would "betray our children and future generations".
"Some may still deny the overwhelming judgment of science, but none can avoid the devastating impact of raging fires, and crippling drought, and more powerful storms," he said.
In the midst of a national debate about gun laws in the wake of the Sandy Hook shooting Obama signalled he intended to try and challenge the status quo.
"Our journey is not complete until all our children, from the streets of Detroit to the hills of Appalachia to the quiet lanes of Newtown, know that they are cared for, and cherished, and always safe from harm," he said.
"We have always understood that when times change, so must we; that fidelity to our founding principles requires new responses to new challenges; that preserving our individual freedoms ultimately requires collective action."
Follow the day's events below: