Compared to the House of Commons vote on Syria, a British referendum vote to quit the European Union would have far more significant implications for the future of transatlantic relations.
The House of Commons decision not to support U.S. military action against Syria, along with opinion polls pointing towards growing public support to quit the E.U., has prompted warnings the U.K. risks isolating itself from both the U.S.A. and the E.U. But focusing on the implications for U.K.-U.S. and U.K.-E.U. relations distracts from the larger relationship Britain's isolationism would affect: the U.S.-European relationship.
The U.S.A. would be left facing an E.U. changed by the disappearance of one of its largest, economically liberal and outward-looking members. Europe's divisions could be deepened, the E.U. and N.A.T.O. weakened and wider transatlantic relations complicated. Alternatively, the U.S.A. could find itself facing a more united E.U., with the U.K. adrift between the two.
An EU in Flux
A British exit could plunge the E.U. into more navel gazing as it negotiates a U.K. exit, and changes its institutions, budgets and policies to reflect the U.K.'s disappearance.
Combined with changes to the Eurozone, the E.U.'s balance of power could shift. The E.U. could become more inward-looking, tending more toward protectionism. Instead of looking out to the Atlantic the union could look more towards the Mediterranean. Smaller states could gain over large states. The Franco-German axis could be unsettled, leaving a more dominant Germany. E.U. enlargement could stall in the face of unease amongst western states at Europe's center shifting further south or eastwards.
On the other hand, rid of a notoriously awkward and non-Euro member, the Eurozone could become the undisputed core of the E.U., pushing the E.U. further towards "ever closer union." Europe's social model could be freed of British attempts to weaken it. Of course, the extent to which Britain's awkwardness can slow the E.U. has been put into perspective by the Eurozone's own struggles to find solidarity and leadership.
Washington would also face a wider Europe changed by the U.K.'s post-withdrawal relationship with the E.U. If the U.K. and other non-E.U. members thrived and the Eurozone continued to struggle, then Britain's withdrawal could trigger centrifugal forces leading other member states to question their membership, in turn unravelling the E.U. But should the U.K. suffer and the Eurozone stabilise, then the U.K. could be further isolated.
Europe Further Divided
For the U.S.A. or Asia, a British withdrawal may reinforce views of Europe as riven by division and decline. There will still be no answer to "who speaks for Europe?" if the U.K. and other non-E.U. European states disagree with the E.U. Europe could become more vulnerable to divide and rule by external powers.
The disappearance from the E.U. of one of its major military powers could further strain efforts at Europe-wide defense cooperation, whether through the E.U. or N.A.T.O. Alternatively, freed of British hesitancy, E.U. defense efforts could be reinvigorated, albeit never destined to reach their full potential without the U.K.
There will be no shortage of applicants to fill London's place of claiming to be America's closest ally in the E.U. While such applicants might not offer a relationship that can claim to be as "special" as that with the U.K., for the U.S.A. they will be of increased importance thanks to Europe remaining an area of the world in which it retains considerable interests.
However, should a British exit further destabilize the E.U., complicate transatlantic relations and threaten the prospects of the Transatlantic Trade and Investment Partnership to enhance transatlantic cooperation in the face of rising powers, then it would only further dampen what hopes Washington still has for Europe to act as an effective partner.
Britain Adrift in Transatlantic Relations
The vote on Syria raised once again the debate about Britain's place in the world, but this is a debate shaped more than anything else by discussion about Britain's place in Europe. This is a debate so persistent and divisive because it goes to the heart of British identity, security and political economy. It is on the issue of Europe that rests so much of the question of what country the UK wants to be.
A decision by the British to answer this question by quitting the E.U. will still leave the U.S.A. facing a Britain struggling to come to terms with its place in the world. Some talk of a vote to quit the E.U. as the means to reclaim Britain's sovereignty, asserting Britain's independence as a "Switzerland with nukes." That those nukes would have to be carried on U.S. built and serviced missiles shows the limits of that independence.
More importantly, Britain would still struggle to assert its sovereignty in the face of a Europe where the E.U. is likely to remain the predominant political actor, and a more important actor in the daily lives of the British than any other state or international organisation, including the U.S.A.
For the U.S.A., a British exit would change both the U.K. and the E.U., forcing it to reassess the relative merits to be given to its bilateral relationship with the U.K. compared to its much larger multilateral relationship with the E.U. Navigating a course between the two is not something any U.S. Administration should relish.