COLOURFUL PAST: Prince Andrew shows President Michael D Higgins, accompanied by his wife Sabina, the colours of the disbanded Irish regiments in the Grand Stairs at Windsor Castle

'States have no eternal friends, only eternal interests." So said Lord Palmerston, a leading 19th-Century European statesman, prime minister of Britain and Ireland on two occasions and landlord of a 12,000-acre estate in Sligo. Palmerston's view is the ultimate realpolitik view on relations between states.

While it goes too far – countries whose peoples share values and many personal connections can and do have important bonds of friendship – it is mostly correct. Interests are always the main determinant in how states behave.

Last week provided further evidence of the normalisation of how the Irish and British states behave towards each other with President Michael D Higgins's state visit to the UK.

Anyone who is concerned about Ireland's interests can only welcome this, given our geographical proximity, dense web of personal connections, mutual concern for peace and stability in the North and very considerable economic interdependency.

These mutual interests can be more effectively pursued when the two states co-operate. And when interests diverge or clash, frameworks are needed to manage differences and conflicts, resolve them if possible, and ensure that any ill-effects are contained and do not spill over to contaminate other parts of the relationship. That is what has happened and continues to happen.

State-to-state relations, as has been repeated almost to the point of cliche, are now better than they have ever been. But nobody should think of this as a happily-ever-after story.

Living cheek by jowl with a much larger neighbour has its eternal difficulties and downsides, as, for instance, Canadians know from their dealings with the US or the Portuguese with Spain or, much more seriously in less pacific parts of the world, Ukrainians with Russia.

Relative power has mattered, and always will matter, a great deal. When big countries act, smaller countries can suffer. An example in Irish-British relations came just last week. A report published by the ESRI on energy concluded "electricity prices in Ireland will increase as a result of unilateral British policy".

This illustrates a wider point. For all the gushing talk last week of a relationship of equals between Ireland and Britain, there will never be a relationship of true equals, given the vast disparity in power between the two states.

Britain is one of only five permanent members of the UN security council. Its diplomatic service is vastly bigger, better resourced and hence more influential. And militarily, though it armed forces are much diminished from times past, it remains one of only a handful of countries in possession of nuclear weapons.

But most important is the economic disparity. Britain is a member of the Group of Seven largest industrialised economies. It membership of that club reflects the size of its economy – still the sixth biggest in the world and 12-times the size of Ireland's.

To note this is in no way to be hostile to Britain – it is a great country I respect, admire and like – but as the wise old saw goes: an té nach bhfuil láidir, ní foláir dó bheith glic (he who isn't strong must be smart).

Being smart for small countries that are heavily dependent on what goes on elsewhere in the world means working against the law of the jungle – which allows the strongest to do as they please – and supporting rules-based arrangements, structures and organisations which limit everyone's scope for unilateral action.

Small and weak countries have more to gain and less to lose by signing up to clubs where everyone is bound by the same rules.

That is why multilateralism – not unilateralism – is the very foundation of Irish foreign policy. We are members of the UN, the EU, the Organisation for Security and Co-operation in Europe (OSCE), and the World Trade Organisation (WTO) to name but a few international and regional organisations.

Among the many reasons it is in Ireland's interests to be in these organisations is because it helps level the playing field with our much bigger neighbour. But there is one organisation we could and should be members of, but are not – the Commonwealth.

Many who applauded the events of the past week would baulk – often very strongly and emotionally – at the prospect of being in the Commonwealth. When asked why, people tend to reject signing up to that club because they believe it would signal subservience to Britain in some way. This says more about a vestigial Irish inferiority complex than how that organisation works.

Countries as diverse as Canada and India are members of the Commonwealth. So are fellow EU members Cyprus and Malta. Even suggesting to citizens of those states that Commonwealth membership in any way amounts to subservience to Britain leads to puzzled looks. Those countries are in the club because it serves their interests – it is a global forum that provides opportunities for contact-building, networking and all kinds of co-operation, from sports to scholarships. While it not a hugely important organisation for any of the 53 countries in it, Ireland actually has a greater interest than most in being a member.

First, there is the benefit of being plugged into another globe-spanning network. This would be beneficial in many ways. For instance, eight of the nine African countries which Ireland's foreign aid programme prioritises are members of the Commonwealth. Irish membership would provide a new forum within which Ireland could interact with those counties, influence them and benefit from relations with them, including commercially.

Second, being in the club would provide another route to access and influence British thinking and decision-making. Because Ireland has more dealings with Britain than any Commonwealth member, this benefit of membership would be commensurately greater.

Finally, and most importantly, a consensus on joining would signal that the largest tradition on this island really has a mature, balanced and realistic view of Britain, the British and Britishness. This would be important for the largest tradition itself – proving that the last vestiges of inferiority are finally banished – but also for the island's minority tradition.

Unionism is currently in a bad place. Demographic change is shrinking the proportion of people on the island who feel, and therefore are, British. Scottish independence would be a hammer blow to the union. The North's economy is based on extreme dependency on English taxpayers' money, which may not always continue to flow across the Irish Sea.

The insecurity of the unionist tradition manifests itself in many ways, not least in that Northern Irish society is becoming more, not less divided – there are now more "peace walls" in Belfast than there were 16 years ago when the Good Friday Agreement was signed. Insecure peoples can easily become radicalised. Some in such communities conclude that lashing out violently is their only option.

We, south of the border, need to do everything possible to lessen the insecurities of both communities in the North. Joining the Commonwealth would not threaten the nationalist community but would signal to unionists that we have replaced irrational and emotive fears about British domination with a grown-up, clear-eyed and hard-headed view on how to relate to our neighbour.

Full and complete normalisation of Ireland-British relations will only happen when there is calm and rational consensus on the Irish side that being in the Commonwealth serves everyone's interests.

Sunday Independent