For Assyrian Christians in present-day Syria and Iraq, religious persecution has been a constant for much of their modern history. The world was reminded of that stark reality Tuesday morning, when Daesh militants reportedly captured dozens of Assyrians -- estimates range from 70 to 150 -- living in villages along the Khabur River in northeastern Syria. Their fate remains unclear, but fit a pattern of Daesh persecution of minorities in areas it seeks to subjugate. "We are watching a living history and all that comprises disappear," Mardean Isaac of A Demand for Action, an activist group that focuses on religious minorities in the Middle East, wrote in a statement published on Facebook. So who are the Assyrians? Alternatively known as Syriac, Nestorian, or Chaldean Christians, they trace their roots back more than 6,500 years to ancient Mesopotamia, predating the Abrahamic religions. For 1,800 years the Assyrian empire dominated the region, establishing one of most advanced civilisations in the ancient world. (An example of this is the city of Arbel, one of the earliest permanent agricultural settlements.) The Assyrian empire collapsed in 612 BC during the rise of the Persians. Then, 600 years later, they became among the earliest converts to Christianity. They still speak an endangered form of Aramaic, the language of Jesus Christ, and consider themselves the last indigenous people of Syria and Iraq. Following the birth of Christianity, Assyrian missionaries spread across Asia, from the Mediterranean to the Pacific, and built a new empire that lasted until Arab Muslims swept through the Middle East in 630. Eden Naby, an Assyrian researcher and Middle East historian, says their modern history has been marred by violence and persecution. Between 1914 and 1918, more than 500,000 Assyrians were killed during the Armenian genocide in present-day Turkey. More recently, the US invasion of Iraq in 2003 and the overthrow of Saddam Hussein, a secular dictator, has exposed Assyrians and other minorities to sectarian strife. Emigration has shrunk the community of Assyrians from about 1.4 million living in Iraq in 1987 to 400,000 at last count, according to Al Jazeera. Others live in Turkey and Iran. About 40,000 Assyrians remain in Syria, according to an estimate from the BBC, a number that experts say is likely in decline. Christians are estimated to have constituted about 10 per cent of Syria's 22 million people before civil war erupted in 2011. Many Assyrians have since fled to escape the ongoing conflict and violent attacks by extremist groups such as Daesh. "These people along the the river are refugees," Ms. Naby says in a phone interview. "They've experienced a hundred years of this." A majority of Assyrians now live among the diaspora in the United States and Europe, including sizable populations in Germany and Sweden. The Assyrians who stayed in Syria are concentrated in Hassakeh province in the sparsely populated northeast. Some have joined a militia, the Syriac Military Council, which fought alongside Syrian Kurds in a new offensive that began Sunday. It was their first major battle against Daesh. Activists say Daesh has forced Christians living in the territory it controls to convert to Islam, pay a religious tax (jizya), or face death. A few weeks ago, the group ordered Assyrians in the area to remove crosses from churches, according to the Assyrian International News Agency. The Assyrians are far from the only religious or ethnic minority group who face such threats from Daesh. Shia Shabaks, Turkmen, and Yezidis have all been targeted as part of the extremist group's campaign in Syria and Iraq, where it has declared a "caliphate". Two weeks ago, a self-declared Libyan affiliate of Daesh beheaded 21 Egyptian Coptic Christians. "These groups have a long history of marginalisation," Sarah Margon of Human Rights Watch said in a testimony to the Tom Lantos Human Rights Commission, a Congressional caucus, in December, referring to Assyrians and other minorities. "But Daesh has intensified this ostracism, labeling them as crusaders, heretics, and devil-worshipers and then threatening them with death if they don't convert to Islam." Experts fear that the Assyrians captured this week could face a similar fate to that of the Egyptian Christians. But Daesh could also use the captives to try to arrange a prisoner swap with Kurdish militias. The extremists are reportedly holding them in Shaddadeh, south of the city of Hassakeh.