Sudden awakenings are often brutal.

Yet we had seen the warning signs: exhortations to spend more on our defence, the pivot to Asia, the red line in Syria, Trump I, the unilateral withdrawal from Afghanistan.

But we thought we had time. That the transatlantic turbulence was a hiccup or a temporary setback. That the world we grew up in could not conceivably collapse in an instant, that we would be given some warning. That we could continue our holiday from history, resting our security on others, ignoring the rules that had governed international relations since the dawn of time.

And then we realise that we have entered a new world.

If we don't want to let others write our history for us, we need to change our software. Very quickly and very drastically. We need to invest massively in defence and technology, simplify our rules, lift our taboos, switch to a war economy and take our European destiny into our own hands. The events of the next few days should make this possible.

The first test is Ukraine.

Because Ukrainians have been dying for the European flag since 2014, because Russia wants to tear down the reunified and democratic European order that emerged at the end of the Cold War. Because Putin's appetite for power will always extend further west, towards the European Union, because we will be next on the list. Because we do not want to live in a world where brute force replaces the law.

There are few cases where our interests and our values come together so clearly.

Our geopolitical Europe begins with support for Ukraine. In abandoning Ukraine, all the opponents of European civilisation, both at home and beyond our borders, will triumph; they have understood this only too well.

Let us make no mistake. This is not inevitable. We can create the conditions for lasting peace and refuse a botched ceasefire, but this will require a long-term commitment from Europeans.

The balance of power is not static; the last few decades have been full of asymmetric wars lost by the great powers. They can be rebalanced by bringing weapons, cash, political will, courage and imagination to bear.

Today's defeatists were yesterday's defeatists. Those who always confuse peace with submission, realism with cynicism, who admire strong men but curiously despise small nations fighting for their freedom. Those who cite the Melian Dialogue, recalling that ‘the strong exercise their power and the weak must yield to them’, but forget that it was Athens that lost the war. Who believe that a new Yalta on our continent will bring peace, when it will only be a capitulation to an aggressive revisionist power that will use it to rearm and prepare the next one, who forget that the first Yalta locked hundreds of millions of souls behind the Iron Curtain.

We know that we are at a historic turning point, but not yet whether it will be the Strange Defeat or Their Finest Hour. It depends on us.