Due to these two splits, when Islam came, it was easy to get Copts to fight against orthodox
Then Catholics and Orthodox disunity led to the losses against the Turks culminating in the fall of Constantinople
Then the Lutheran v/s Catholic v/s Calvinist struggle diverted resources from fighting the turk, and culminated in 1683 with Calvinist Hungarians fighting on the side of the Turk against Christendom (nationalism at rise)
You then had the French competing with the GErman Empire to be "the friend of the Moslems" and the English doing that the best (they enabled teh Wahabbi take over of Saudi arabia, that led to Al qaeda, the taliban, al-shabab, the islamic state, boko haram etc. + they also created Pakistan and caused the Palestinian problem)
Christian disunity is the constant theme throughout history which has led to Islam WINNING 3 times (in the 7th century, in the 15th and in the 16th and 17th).
If Christendom had remained united (and I see Catholics, Lutherans, Anglicans, Calvinists, Orthodox etc. all to blame in some way or the other) or at least saying "I will suspend my animosity to other people who believe in Jesus Christ as Lord, GOD and Savior to fight those who don't" -- if we hadn't been disunited, Islam would still be concentrated around the Mecca-Medina area
Islam is an anti-Christian movement. You have just detailed how disunity has enabled the rise in our day of the worst threat to Christianity in our world today which is perpetrating the worst persecution of Christians today.
Heresy should be so lucky.
Divide and conquer still works.
Disunity is a problem in Catholicism; too.