Increasingly, it seems, only scar tissue keeps the European Union together.

Early this year, efforts to keep Greece from going bankrupt and within the 28-nation EU ripped open an ugly north-south divide. Now, the migration crisis — and the question of whether Europe should be a more welcoming continent — is creating a new east-west breach.

"I fear we are starting to rebuild invisible, new Iron Curtains across Europe," said EU Commissioner Johannes Hahn.

Over a punishing year, the two crises have focused the 500 million citizens like never before on one question: Is unity worth it? So far, as nations plod from one unwieldy compromise to the next, the answer remains — just barely — "Yes."

After all, this is the same European Union that only three years ago won the Nobel Peace Prize for its half century of efforts in molding former enemies into a tight political bloc where reconciliation was an article of faith, and ever-tighter union almost a foregone conclusion.

The 28 nations still take a great many decisions independently, ranging from defense issues to taxation. But over the years, joint action for one bloc in a globalized world has been the only way to stay relevant.

Now, a different reality is setting in.

Hundreds of thousands of people, many fleeing war and persecution, are knocking on the EU's doors for shelter, drawn by Europe's wealth and its traditions as a land of asylum.

As it turns out, even if countries like Germany, Sweden and Italy have largely lived up to expectations, others with weaker economies and fewer traditions of immigration have turned a cold shoulder. New EU members like Poland, Slovakia and the Czech Republic reject to any notion of mandatory shelter for refugees to ease pressure on other EU nations.

Hungary, another EU newcomer, has been at the center of the storm, using fences, razor wire, tear gas and water cannon to keep refugees from pouring across the border from Serbia. That has forced thousands of migrants to seek a new route through Croatia, raising cries of alarm from Slovenia and Austria.

The constant scenes of one country trying to shift the burden to another, often with great acrimony, have sorely tested the vision of Europe as a united continent.

"This is one of the biggest challenges that we have had in Europe for decades," said German Chancellor Angela Merkel.

Much like during the Greek financial crisis this past spring, in which Athens and Berlin bickered incessantly over money and historical rights and wrongs, tempers are flaring again among countries that should be bonding.

Even Luxembourg Foreign Minister Jean Asselborn, who should be a neutral party, since he presides over EU meetings on migrants, could not contain himself this week.

"Even a little country like Luxembourg is able to accept a few hundred people who are not of Christian religion, who have another skin color, and this should also work in big countries like Poland or the Czech Republic or Slovakia, for example," Asselborn said.

And western EU nations like Germany and Belgium have hinted that eastern member states should be financially punished — with a suspension EU financial support — if they refuse to do their part.

"It is a crash test for Europe, a crash test for our values," said EU Migration Commissioner Dimitris Avramopoulos. "Some countries are thinking rather in a national than in a European way."

One of the problems coming to haunt the EU is that, through much of its history, it has launched into projects head-on, without all the legal minutiae settled beforehand.

For example, European leaders agreed on pushing ahead with the euro single currency almost two decades ago, despite the lack of watertight answers about how countries with widely different financial and economic policies would manage using one currency.

When Greece's finances collapsed, the lack of a solid plan almost caused the eurozone to break up.

Similarly, EU nations set up their first tentative common asylum policy in 1999, with little idea of the real challenges facing them. The lack of foresight is again driving EU divisions, as countries push different visions of how to deal with the refugee crisis.

"EU reality has been to solve problems when they are in your face, because the real solutions are often tough to sell to public opinion," said Prof. Hendrik Vos, Ghent University's EU expert. "It is left to improvisation."

So often on the continent, however, the public has been very meek on all things EU, with often fundamental issues pushed through by bureaucrats with hardly any debate among the population. Britain was often the lone exception, as a strong Euroskeptic grass-roots vanguard kept sovereignty matters at the top of the agenda.

This is what makes 2015 such a watershed. With the euro crisis and the threat of Greece being kicked out, public opinion throughout the 28 member nations has focused on the EU day in day out, for weeks and months on end.

It is no different with the migrant crisis, as the prospect of an endless array of EU meetings looms large again. "Suddenly, Europe is at the heart of the public debate," Vos said. And the extra attention makes solutions even tougher.

Even if the EU navigates this crisis too, there will be no rest. The next text will be Britain's referendum, which must be held by 2017, on whether it wants to stay in the European Union.

All three issues left European Commission President Jean-Claude Juncker with little enthusiasm during his State of the Union address last week.

"Our European Union is not in a good state. There is not enough Europe in this Union," he said.

"And there is not enough Union in this Union."

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Raf Casert can be followed on Twitter at http://www.twitter.com/rcasert