Well if you watch Sheikh Imran Hosein, he gives an Islamic eschatologic view on why this is. Basically the Anti-Christ starts his mission from Western Europe (specifically Britain). Therefore in his view the Orthodox Christians of the West were overtaking by "Anti-Christ" Christianity and over many centuries, now you have "Christian" nations allowing two men to marry one another plus everyhting else like fighting anyone who stood in the way of his mission, one example was Christian Russia. They succeeded when the USSR was established and they were finally about to kill Russia off, when they destroyed the USSR, but they plan and so does God.
It is interesting to note that the Orthodox Britons suffered immensly at the hands of the "Papist" Normans and England was taking away from Orthodoxy after 1066 (this is the view from a British Orthodox former diplomat, I forget his name, but will try to find it for you) then you have further schisms from the Papacy leading to the Anglican Church and destruction of Monasteries etc and then finally Britain becomes the ruling state in the 19thC and is secular and gives "birth" to Israel.
Orthodox Christianity and Islam were and are the two forces that oppose the Imposter Israel and the Anti-Christ, hence why the Anti-Christ and his civilization fought and fights against them.
I cannot do justice to the subject with my words, but if you have time please watch his Sheikh Imran Hosein's vides, he even went to Moscow university and gave a lecture there and discussed with Orthodox priests.
Constantine was born in what is Serbia now.
Yes the original Romans were arian but todays Romans are not as "pure".
Have you read this?
https://chechar.wordpress.com/2016/12/13/aryans-who-no-longer-want-to-live/