Maybe not the newer more liberal version of Christianity but historically Christianity was nationalist, militaristic, assumed it's supremacy, under one authoritarian God.
I understand there are liberal Christians but this seems a change from the past.
I disagree that it has been historically nationalistic. Certainly the teachings of Jesus making a clear distinction between national identity and spiritual faith, "render unto Caesar that which is Caesar's, and render unto God that which is God's," gets flattened out in a Christian nationalist's mind. The flag, national identity, and belief in God are all part of the same thing. That was not what Jesus taught, ever.
The specific question in your OP is this. "
Is the Christian God a Fascist?" The answer is definitely not! Even if the church got in bed with the State at some point, which it did, that is still not Christian Nationalism. It's something else. It's a State religion. That's not the same as nationalism, which is about identity-politics conflating worship of God with worship of the state.
Edit to add:
And to add one thing here, no, it is not liberal Christianity that is against Christian Nationalism. Many conservative Christians are as well. Baptists, are not liberals, and that article I linked to in my thread is from a Baptist minister. Here is a good article from the Methodist church about Christian Nationalism as well. I don't thinks there are considered left wing, progressive arms of Christianity. Do you? Both conservative and liberal Christians view this as a distortion of Christianity.
What is Christian nationalism?
BTW, the above link is a good read. I'd very much recommend reading it.