Egyptian Christians make up about 10% of the population, and their suffering is an underreported result of recent political turmoil. This New York Times report fills in some of the details. In brief, Christians have been targets of Islamist hostility for some time. After the army attacked the pro-Morsi protest camps, killing hundreds, Islamists throughout Egypt reacted by burning churches and attacking Christians. (Christians had, indeed, backed the army in its takeover from Morsi–and they made visible, unprotected targets.) While these attacks went on, the army and the police did nothing to stop them.
Now the army is trumpeting the persecution of Christians as evidence that the Islamists are terrorists. They do not mention that the army made no attempt to stop this terrorism.
The article ends with a brief mention of a single Muslim who stood up to the mobs at the risk of his life. Apart from such heroic individuals, no one seems willing to defend Egyptian Christians.