With armed police outside and CCTV cameras within, St Joseph's Chaldean Catholic Church in Baghdad does its best to protect its worshippers from the dangers of modern-day Iraq.

But as the rows of empty pews show, most of its congregation have opted for altogether safer sanctuary abroad. Of the 5,000 families that the church once tended to, only 150 now remain after a mass migration in the last decade to Europe and America.

"They feel there is no peace, law or justice here in Baghdad, and that our country has become a land of militias," said Father Nadheer Dako, St Joseph's parish priest, after a Sunday morning service that drew just 25 people to a church built for 1,000.

Father Dako has just returned to Baghdad after a six-year posting to the Holy Family Roman Catholic Church in Ealing, west London, where many exiled Iraqi Christians now live. His flock there is now 350 families strong - more than twice what remains in Baghdad.

The shrinking parish at St Joseph's - one of only a handful of churches now open in Iraq's capital - is just the latest sign of the mass exodus of Iraq's Christian population. In the lawlessness and sectarianism that has prevailed since the fall of Saddam Hussein, nearly four fifths of the 1.5 million-strong community have left, and in recent years, church leaders have warned that a time might come when none were left at all.

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They had hoped that the defeat of the Islamic State in Mosul and gradual security improvements in Baghdad would have stemmed the tide. If St Joseph's is anything to go by, however, the mere prospect of a future free of car bombs and kidnap gangs is no longer enough to make people stay.

"It is true that people are no longer getting kidnapped as much, and the Islamic State is gone," said Nasib Hana Jabril, 42, a St Joseph's parishioner. "But the infrastructure of the country has been ruined, and people want a better future, not so much for themselves but for their children."

The exodus is less pronounced in northern Iraq, where some have now returned to historic Christian-majority towns like Qaraqosh, which was over-run by the Islamic State in 2014. But while there is a determination to maintain a foothold there - Qaraqosh was first settled by Christians in the 4th century - there is more nervousness about Baghdad, where Christians are now a tiny minority.

Quite aside from the capital's big city crime problems, religiously-mixed Baghdad is still likely to be the first flashpoint for any renewed sectarian violence, which saw several churches attacked a decade ago. Unlike Iraq's Muslims, the country's Christians also lack traditional tribal networks, which act as rallying points for self-defence.

"We have no tribe here, so if things go wrong, there is nobody here to help us," added Mr Jabril. Another problem, though, is that for many families, a tipping point has simply been reached where more of their relatives live outside of Iraq than inside.

When regaled with tales of how much better life is in the likes of Britain, Sweden or the US, it is hard not to feel tempted. It is not just about fears of persecution, but more mundane concerns like the absence of decent schools, according to Father Dako.

"Returning here from London after six years, I've noticed how the quality of education in Baghdad has gone down in nearly all the primary schools," he said. "The new generation just have very little hope of making a life here anymore."

Exactly how many Christians still live in Baghdad is not known, although in Father Dako's district of Karrada - one of three main Christian neighbourhoods - there were originally 10,000 families.

The fear is they may now end up like the city's Jewish community, which died out altogether after Ba'athist pogroms in 1969. Calls by local bishops to tough it out and preserve the city's Christian heritage have met with accusations of hypocrisy.

"A lot of the bishops have sent their own families abroad," said Hana Samoul, 45, whose nephew was kidnapped and murdered by a militia, and who hopes to move to Detroit. "Why should they expect us to stay?"

One parishioner who has heeded the bishops' call is Mahran Avedisian, an engineer, who has decided to stay despite having siblings in Canada, the US and Sweden. "I love my country, and if I left, the candle of our religion would be going out," he said, after attending a recent Sunday church service at St Joseph's.

He hopes that his four young children - dressed in their Sunday best clothes - will grow up as part of a new generation of Baghdad Christians.

But whether that prayer will be answered, even Father Dako does not know. "Will there still be a Christian community here in Baghdad in 2050?" he said. "That is hard to say.