This photo sums up how much the world has changed in 2016

We can all agree that 2016 was the year anti-establishment politics became mainstream in the West, sending shockwaves across traditional political parties.

One photo taken in April at the G5 in Hanover pretty much sums up this sentiment.

It shows Angela Merkel surrounded by Matteo Renzi, Francois Hollande, Barack Obama and David Cameron -- the then-leaders of Europe's four largest economies and the United States.

The photo re-surfaced on Twitter after Renzi's shock resignation on Sunday night, following a crushing defeat in Italy's constitutional referendum:

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The smiling faces betray naivety and unawareness of what will come next.

David Cameron was the first casualty of the populist uprising against the establishment, forced to resign in June after losing the Brexit referendum in Britain.

Barack Obama is perhaps the only one among them to enjoy record approval ratings and was going to leave office in January anyway. But Donald Trump's victory at the U.S. presidential elections risks undermining his legacy.

Francois Hollande said last week he wouldn't stand for re-election in France after just one term.

And finally, Matteo Renzi just announced his resignation as the Italian prime minister after losing a constitutional referendum by a landslide.

The last leader standing is Angela Merkel, who will seek a fourth term as German chancellor next autumn.