A recent headline on the leading French newspaper Le Monde said it all: "Migrants, the Euro, Brexit: The European Union is mortal." And it's true. The EU could actually collapse over these three threats.
The most immediate threat is "Brexit" (British+exit), the possible result of the yes/no referendum on British membership in the EU that is scheduled for June 23. Prime Minister David Cameron promised this referendum three years ago mainly to placate the anti-EU faction in his own Conservative Party, but it is coming at a particularly bad time.
Cameron doubtless calculated that the referendum would produce a large majority for staying in, which seemed a safe bet at the time. But the vote is actually being held at a time when many English people are upset by the large flow of immigrants into the United Kingdom and blame it on the policy of free movement for EU citizens.