What was the MOST IMPORTANT TREND OR EVENT of 2015?

Any wide, major conceptual changes due to events?

The rise of Isis.

Bruce Jenner turning into that thing.

Blacks uprising against the police violence and murders of them.

Internationally:
The takeover of the Syrian civil war by Russia and sidelining of USA.
The Deal between the P5+1 and Iran.
Locally: the replacement of Tony Abbott by Malcolm Turnbull as Prime Minister.

I'd probably have to say the growing threat of fascism and the rising danger of the right. The far right has been gaining ground all over the world in recent years. There are a few particular hotspots, namely Ukraine, Japan, Greece, India, the ISIS-controlled parts of the Middle East, but there are also worrying signs in the US (where the police are becoming increasingly vicious and oppressive, the KKK seems to be making a comeback, Islamophobic bigotry and racist violence are skyrocketing, and we have a mainstream presidential candidate, Trump, sounding remarkably like a fascist and gaining a wide following) and in Europe in general, particularly France. Leftists and progressives have been losing ground lately, with a progressive government coming to an end in Argentina, the capitulation of SYRIZA in Greece, and counterrevolutionaries winning a parliamentary election in Venezuela (though the left is still strong there, fortunately; this was only a setback). The worst thing though is Ukraine, which is the first case of outright Nazis holding state power in seven decades. That's probably the most dangerous thing happening in the world now, even worse than ISIS.

There are good things happening too though, there's some pushback, such as the rise of the Black Lives Matter movement in the US, a growing opposition movement in Japan against the Abe government's militarism, a massive anti-corruption campaign in China, the Houthi revolution in Yemen, and perhaps most importantly, Russia's intervention in Syria possibly saving Assad's government and turning the tide of the war against the takfiri fascists of ISIS and the FSA.

But i'd say the definitive trend of the year is the growing danger of the far right.