There are moments in politics when various historical strands meet in a single event, with repercussions bigger than anyone could have predicted just hours before. Last night we had one of these moments.

Britain just got bigger and smaller.

Bigger because it acted to sever its relationship with America. The special relationship has always been uniquely unhealthy for both countries. We offer them a veneer of international legitimacy which they do not have. They offer us a mirage of global strength which we do not deserve.

American foreign policy simply cannot be relied upon to do the right thing and we have found ourselves bogged down in several moral abominations because of our insistence on clinging to their coat tails.

Even Harold Wilson, who kept Britain out of Vietnam despite fierce American threats, could not bring himself to condemn it. Asked by student protesters why he wouldn't go public with his criticism, he replied: "Because we can't kick our creditors in the balls."

Barack Obama, whose grandfather may have been tortured by the British, has no emotional connection to these islands, unlike his predecessors. That is more of a blessing than a curse. It gives us the chance to break away. We should take it, before another phoney Anglophile republican comes and rubs our bellies and says all the right words and we pack our sons off to another pointless imperialistic war.

Our alliance with America – from the purchasing of British spying operations to the humiliation of our prime ministers as they fawn over their Atlantic counterparts – belittles us as a nation. As in Europe, we stand taller if we stand apart. Yesterday was an important milestone in making that journey.

But we are also bigger because our parliament has demonstrated its strength, in front of an international audience. Parliament is one of those words which you rarely consider in its full glory. It now conjures up images of tourists posing for photos by Big Ben. In fact, it is one of the most remarkable creations of political struggle. It has challenged and killed kings.

Through a mixture of planning and accident, it has become the vehicle by which the people challenge executive power. Yesterday it effectively acquired a veto – according to the shifting rules of Britain's unwritten constitution – over military conflict.

In the US, Congress begs for a debate. In the UK, parliament has one and ties down the executive. British parliamentary democracy, under a symbolic, non-political head of state, remains the most effective and versatile form of governance in the world.

But yesterday also shrunk us. It showed we are not willing to step in when tyrants abuse their people. It showed that austerity, unjust wars, and the suspicion of the political class have made us hesitant in the face of horror.

It is tragic that Tony Blair's decision to take us into an unnecessary war, to twist evidence to his liking, to lie to parliament and the British people, has robbed us of our willingness to help other countries. This will be his political legacy – not just staining the reputation of Britain overseas, but staining it in the minds of those at home as well.

This country's economic and military strength means it has a moral duty to help the poorest and weakest where it can. We have a lot to make up for. The empire and its various abuses are our legacy and one we can only live down by helping those who need it.

We should be wary of what happens when Britain becomes self-centred and inward looking. Some of our greatest betrayals came not via action, but inaction.

Wilson, the master strategist, ruled out force against white supremacist Ian Smith in Rhodesia. This blunder should be taught to schoolchildren as a supreme act of British cowardice and irresponsibility. Our indifference to the fate of India when we decided we couldn't afford it any more caused the deaths of up to a million people during partition and grievances which could still end the world in nuclear war.

This is a strong country. Not as strong as it once was, but still comparatively influential. What we do is important, no matter how much the British like self-deprecating about their role in the world.

The UN is a car at a standstill. If the only legal action is one with the consent of the security council, there are very few meaningful legal actions. There must, of course, be reform of the security council but until then those that can bear a responsibility must do so for those who need them to.

To stand aside and do nothing when dictators kill their people is not anti-imperialism. It is barbarism. It is a conspiracy in defence of the strong, because it refuses to stand up for the weak.

Of course, there are other factors in Syria, not least escalation and end goals. But last night's vote was not about military action. It was about condemnation, and yet still we shrunk away from it. It was a statement of intent from parliament and, to very genuine, worrying extent, the public: We are shrinking away from our traditional role in the world.

Yes, our foreign policy is beset by moral inadequacy. Yes, our arms industry often overrules our ethical instincts. The solution to these problems is not to give up on morality. It is to introduce it to our trade and diplomatic missions as well.

Yesterday was a very big moment for us, in which some very positive developments took place. It is typical of the bittersweet irony of history that it should happen in such a depressing way.

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