A century, a hundred years, a ton: whatever it is called, those two zeroes make it an irresistible measure, big enough to serve as a yardstick of human activity, not so great that the consequences of events beyond a human lifespan are fully comprehended. This year, 2016, feels unmistakably like a watershed, a point of departure to which future historians will return again and again in search of explanation and illumination. Brexit, Trump, these are events all the more shocking for their causes afterwards being so apparently plain to see. But moments in history often move swiftly from the astonishing to the blindingly obvious.

The year that starts this Sunday, 2017, is the centenary of another year like 2016, a year that also marked an irreversible shift in the world order. The political world and, with it, the human imagination were reconfigured in ways that were sometimes instantly obvious – the two Russian revolutions in February and October, for example, or the dawn of total war marked by unrestrained U-boat attacks on allied shipping and the first bombing raids on civilian London.

But the full ramifications of other developments – the Balfour declaration, for example, also in 1917 – did not become clear for a generation. Even now the pattern of the mosaic that emerged with the twisting of the kaleidoscope in 1917 is open to reassessment: see, for example, an essay by the historian Adam Tooze in this month’s Prospect magazine in which he describes the end of the American century, the 100 years of dominance of the idea of liberal democracy that began with US entry into the first world war in 1917.

Often what seems obvious can also mask other significant changes. The Bolshevik overthrow of the first, feeble attempt at parliamentary government in Russia, or the extinguishing of all prospect of a negotiated peace after the entry of the US into the war, never ceased to be the defining events of the year.

But only later can it be seen how revolution in Russia coincided with and gave heart to the development of radical nationalism in China and India. And, while radical movements in Europe took their cue not only from Bolshevism but from the message it carried about the possibility of change, the fear of the contagion of revolution led to the rise a reactionary and nationalistic right. Only hindsight reveals how Bolshevism in Russia slowed the prospect of a liberal reform of Europe’s imperial powers; as Professor Tooze points out, 1917 was not just a year of revolution, but the year that the precursor of the Nazi party was founded.

And only with its collapse, 25 years ago this week, did it become clear how communism froze diverse popular movements throughout the Russian empire. It was the thaw in the permafrost after the red flag was lowered over the Kremlin that exposed old nationalist divisions from Azerbaijan to Georgia.

It is not only that more subtle changes on the landscape of the past are exposed. As real memory fades, other narratives expand in its place. Images, like Paul Nash’s Menin Road, first conceived early in 1917, and the written word, like the poems of Wilfred Owen, which were powerfully influenced by a meeting with Siegfried Sassoon that year, came to replace the tales of glory. History can be used, and abused, but the historian’s eye always plays a part in translating the present.