Now that Croatia has become the 28th member of the European Union, there is plenty of talk that the European house is "full" and that no more members are desirable. It is undoubtedly tempting to keep the other Balkan countries on the sidelines of Europe.
But is it realistic to expect Europe to prosper as long as it has a soft underbelly where drug trade, human trafficking and money laundering are rampant – and where three powerful geopolitical forces (the West, Islam and Russia) meet?
The seeds of conflict in the Balkans will not be eradicated until the region, like Southern Europe in the 1980s and Eastern Europe in the 2000s, is safely anchored within the European Union.
At a time when "EU Europeans" have to contend with a lot of worries, Croatia's accession last week – like Estonia's recent adoption of the euro – provide a moment of positive sentiments. Those sentiments underline the enduring and remarkable attractiveness of the European Union and indeed its huge long-term success.
On a less positive note, we have to be mindful of one of the world's most unpleasant anniversaries – that of the beginning of World War I. On June 28, 1914, with the assassination in Sarajevo, that world war was set into motion.
A century onward, the EU accession of Croatia on July 1, 2013 redraws the borderlines of Europe more or less to where they were in 1914. The anniversary thus reminds us of the inability of Europe to fully heal the wounds of a conflict that left it in ruins with millions of dead and led directly to the Bolshevik revolution and World War II.
What is called, in current Euro-speak, the Western Balkans is as divided today as it was in 1914. Most unsettling, the position of Bosnia is practically equivalent to what it was then – a sort of European, rather than Austro-Hungarian, protectorate ruled with limited local participation.
In the past decade or so, the Western Balkans have been relatively tranquil. They have thus disappeared from the public eye – and, it would seem, from the interests of ordinary Europeans.
They have faded from the attention even of those in the European Commission who are paid to continue, however reluctantly, various partnership or candidacy negotiations with the six countries of the region: Albania, Bosnia, Kosovo, Macedonia, Montenegro and Serbia. The latter three are officially "candidate" countries with negotiations that have either not started or move at glacial speed.
The troublesome fact is that none of the six countries in the Western Balkans have solved their border issues, ethnic relations or corruption. While the violent conflict has receded and another outbreak is unlikely to be repeated soon, the problems have merely been postponed.
Economic growth in the Balkans in the past decade, with the exception of Albania, has been anemic. The levels of incomes of all countries in the region remain significantly below the EU average (under $10,000 per person against almost $30,000 for the EU).
The countries' current income levels are, moreover, often below the peak incomes previously achieved: Serbia's GDP per capita today is equal to its 1975 level; Macedonia's is no higher than in 1979; Bosnia's is only 20 per cent above the 1980 level.
While democracy, in the sense of free media and generally fair and free elections, seems relatively safe (despite periodic voting disputes, as recently seen in Montenegro), progress on the rule of law has been minimal.
This leads us to the wider European conundrum: I am not referring to the euro and the potential fiscal, banking and political union. The long-term future of Europe will only be secure when the remaining Balkan countries have become EU members. Only that will make their unresolved border issues and potential ethnic conflicts truly manageable.
Only as EU members can this collection of small and barely viable countries have a chance to grow faster economically and eventually catch up with the rest of Europe. The shift will help people living in these countries overcome centuries of narrow-mindedness, with sharp outbursts of conflict reaching even the global stage.
A Europe that is generally hesitant to get much involved in the wider global security infrastructure must at least take on the settlement of the Balkans issue. Even if that requires a considerable leap of faith on the part of "mainstream" Europe, its own well-understood self-interest and sharp historical markers should dictate that.
Thus, it is both security and economic reasons that dictate the need for the EU to include the Balkans. The sooner this is done, the faster Balkan countries will converge to European standards. This process begins with the rule of law and extends all the way to economic development.
So much for what is right and good. The problem with this grand theory is that never has the time been less propitious in practice to call for further European enlargement. EU enlargement fatigue is palpable, both among the public and the politicians.
Perhaps Europe wants to treat the Balkans the way the United States treats Central America: with general indifference, emphasis on drug trade interdiction and allowance of some moderate migration.
But this does not really seem a useful analogy. Geographical and political distance between the United States and Central America is much greater than between Europe and the Balkans. The geopolitical stakes are entirely different too.
Moreover, standard U.S. policy toward its southern neighbours has been one of forgetfulness and neglect, benign or otherwise.
The promise of the European Union was different. But as it is, Europe would be unprepared, perhaps as much as in 1991, for the breakout of another Bosnian war.
Hard though it may be to imagine, neither a conflict between Serbia and Kosovo nor a civil war in Macedonia can yet be entirely excluded.
It would thus make much more sense for Europe to take a longer-term view and to move forcefully towards speedy integration of the Western Balkans. Then, within a decade, it should move to allowing yet an even greater geopolitical change, the accession of Turkey.
But while these seem most desirable as goals, they are hardly likely to be achieved in the current European political climate. In fact, it is not an overstatement to say that these objectives have never been further from realization.
So let's remember this: When European leaders meet in a year's time on the bridge in Sarajevo where Archduke Franz Ferdinand's assassination in 1914 launched a pernicious world war, they will be toasting to a Europe that, a century on, is still not yet whole.
Branko Milanovic is a contributing editor of The Globalist, where a version of this article originally appeared, and Professor at the School of Public Policy, University of Maryland.