German Chancellor Angela Merkel greets France's President Francois Hollande, (2nd R) U.S. President Barack Obama, Prime Minister of Great Britain David Cameron (L) and Prime Minister of Italy Matteo Renzi (R) at Schloss Herrenhausen palace on April 25, 2016 in Hanover, Germany.

Here's a good example of how much global politics has changed in 2016. Back in April, leaders of the G-5 group of leading industrial nations sat down for a round-table discussion at a summit in Hannover, Germany.

A bit more than six months after, only one of the world leaders looks set to stay in politics - for now.

David Cameron resigned last June after losing a referendum where Britain chose to leave the European Union.

Barack Obama is leaving the White House in January after a shock vote last month where the Republican nominee Donald Trump was elected the next president.

ChancellorAngela Merkel is facing a key election early next year. Apart from new opponents on the left, Merkel has to deal with a growing support for anti-euro and anti-European populism parties and criticism over her refugee policy.

Francois Hollande announced last week that he would not seek a second term as French president given his low popularity among the electorate.

Matteo Renzi is handing in his resignation to the Italian president on Monday after losing a key constitutional referendum.