>> Christians also believe in one God.
You could get a Ph.D. in Theology arguing that one, either pro or con.
Not true. Christians believe in only one God. Indeed, that is the opening line of the Creed recited at the Mass: "I believe in one God…" The question of the Trinity is of the nature of God, not the number of gods. You could argue that it is false but you cannot argue that Christians believe in three gods.
Indeed, that is one long involved argument with no end. A certain preacher said stay away from useless arguments that cause divisions, but rather put on humility, love and a contrite spirit. He is a respected teacher, who wrote a few books in the compilation we call the Bible. Not only that, but the argument goes beyond the Christian realm. Schma Israel, Adoni Elehenu, Adoni Echad. I have heard that the Schma itself is a definitive statement to settle this very issue. (Hear O Israel, the Lord your God, the Lord is one...) In other words, God, the Messiah and the Spirit are One. But the Rabids don't hear it that way. They hear that God is one, so how can He be three? Ironic... Those who will not see, cannot see.