The European Union is being battered by a perfect storm of crises that threaten to rip apart the peaceful and prosperous 28-nation bloc that rose from the ashes of World War II.
It is grappling not only with the threat of a British exit, or "Brexit," but also with an unprecedented migrant influx, continued fallout from the debt crisis and an array of security threats, both domestic and foreign.
- 'Brexit' -
Britain's possible exit from the bloc may be the most imminent risk. Prime Minister David Cameron is demanding controversial reforms of his peers in return for persuading Britons to vote to stay in the bloc in a likely June referendum.
European Council President Donald Tusk, who chairs a two-day EU leaders summit in Brussels from Thursday, has been touring European capitals in a bid to forge a deal that is supported by the member states.
But opposition to British demands remains strong.
A key sticking point is an "emergency brake" that would allow Britain to limit welfare benefit payments for four years to workers from EU countries in Britain.
Central and Eastern European countries like Poland and Romania complain the plan would discriminate against the large numbers of their citizens who work in Britain and undermine the core EU principle of freedom of movement.
Others such as France, meanwhile, oppose Cameron's demands for non-euro Britain to have special safeguards to ensure its lucrative finance sector in the City of London does not suffer as the 19-nation single currency bloc binds closer together. Paris has made very clear it is totally opposed to anything which would give London a veto over eurozone decisions.
- Migrant crisis -
EU member states are sharply divided over how to cope with the biggest movement of refugees and migrants since World War II, after more than one million arrived in the bloc last year, mostly from Syria and other war-torn countries.
The pressure is prompting member countries to build fences or reintroduce checks at internal borders that threaten to eliminate the passport-free Schengen zone, a hallmark of European freedom and unity.
The EU's cherished principle of solidarity has so far failed to make itself felt as the European Commission struggles to get member states to relocate 160,000 asylum seekers from frontline countries such as Greece and Italy.
Eastern European states are among the most prominent opponents of the plan and are pushing efforts to bolster EU external borders, such as in Greece, which is the migrants' main gateway to Europe.
- Eurozone debt crisis -
The eurozone debt crisis, which peaked in 2012, has left several southern member states economically devastated, especially Greece, piling on the misery in an area which is also hardest hit by the migrant crisis.
While debt-laden Greece finally got a third, huge bailout in July after months of bad-tempered negotiations, analysts say many of the single currency's underlying problems remain.
Greece's colossal debt is probably unsustainable, analysts say, but getting it reduced is proving very difficult as creditors demand more painful reforms before they will cut Athens any slack.
Portugal received a massive international debt bailout in 2011 that saved it from defaulting, but in return the country has also had to introduce a string of unpopular austerity measures now repudiated by voters.
Many other eurozone countries have also suffered, as national debt levels nearly everywhere have increased sharply.
Recent signs that the single-currency economy is slowing, buffeted by global market turmoil and concerns over the China outlook, are clouding the prospects.
- Security threats -
From Russia's intervention in Ukraine, to the spread of the Islamic State group on the continent's southern and eastern periphery, to terrorist attacks in European capitals, the EU is facing a major string of security threats.
Poland and the EU's small Baltic member states fear Russia may want to reassert its Soviet-era control over them, with no sign of a lasting peace taking hold in Ukraine.
Clashes between pro-Russian separatists and government forces in eastern Ukraine have claimed more than 9,000 lives since April 2014.
The EU is meanwhile trying to bolster efforts to solve the apparently unending war in Syria and to establish a national unity government in Libya, where Islamic State jihadists have recently made some significant ground.
IS claimed responsibility for the November 13 attacks in Paris that killed 130 people and wounded hundreds more.
The EU is behind member state efforts to boost security and staunch the flow of an estimated 5,000 Europeans who have joined jihadist groups in Syria and Iraq, some of whom have returned to Europe to launch attacks.