Joe Biden has been inaugurated as the 46th President of the United States after a ceremony in Washington DC.
The Biden Presidency marks a new era not just for the US, but also for the rest of the world.
After four turbulent years, Donald Trump has left the White House and Mr Biden now have faces a number of issues, including COVID-19, the drawdown of US troops in the Middle East and huge levels of division across the country.
The inauguration unfolded at a US Capitol battered by an insurrectionist siege just two weeks ago.
Taking over a 'fragile' democracy
On 6 January, the outgoing president’s supporters stormed the Capitol in an attempt to prevent the certification of Mr Biden's victory.
The incident – which sent shockwaves worldwide – underlined the polarised political and sociological standpoints across the country.
Presidential historian, Michael Beschloss, said: "Biden will face a series of urgent, burning crises like we have not seen before, and they all have to be solved at once. It is very hard to find a parallel in history.
"I think we have been through a near-death experience as a democracy.
"Americans who will watch the new president be sworn in are now acutely aware of how fragile our democracy is and how much it needs to be protected."
Tackling the pandemic
One of the main challenges the new US President will face as he takes office is how best to deal with the pandemic.
In an effort to reduce the spread of the virus, Mr Biden is requiring the use of masks and social distancing in all federal buildings, on federal lands and by federal employees and contractors.
He is also challenging all Americans to wear a mask for the first 100 days of his administration.
That is a critical period since communities will still be vulnerable to the virus even as the pace of vaccination increases in pursuit of Mr Biden’s goal of 100 million COVID-19 vaccinations in 100 days.
More than 400,000 people in the US have died after testing positive for COVID-19.
Members of the public have been asked to stay at home during the inauguration in a bid to prevent the spread of the virus.
Deciding what to do in Afghanistan
After being sworn in as the 46th US President, Mr Biden has also become the Commander in Chief of the planet’s mightiest military.
The US military is made of more than a million service personnel, with a world-wide footprint – including 10,000 servicemen and women in the UK.
As he takes over as president, Mr Biden will be in charge of more than a dozen combat and counter-terror military operations.
He will also need to make a rapid decision about the situation in Afghanistan.
Mr Trump has already withdrawn most US troops from the country and committed to getting Britain and other NATO allies out by May.
However, the Taliban do not appear to be complying with the peace deal commitments and NATO has set out a deadline of next month to decide what the alliance will do.
The US has also withdrawn the majority of its troops from Iraq with just 2,500 troops remaining in the country – the same figure that is in Afghanistan.
The US on the world stage
Mr Biden faces the same external threats and challenges as his predecessor, but his approach appears to be very different and more conventional.
He has promised immediate positive actions, such as re-joining the Paris Climate Agreement and the World Health Organisation.
He has also pledged to re-join the international deal limiting Iran’s nuclear technology, also known as the Joint Comprehensive Plan of Action (JCPOA).
However, since Mr Trump quit the JCPOA in 2018, Iran has since advanced to one step away from weapons-grade uranium.
Mr Biden also inherits an urgent deadline with Russia to renew the one nuclear weapons treaty shared by the two countries.