Eheu, I hate for this to be my first substantial post, but this is an atrocity. Fools, I tell you, fools.
For the original question - it depends. You see, along time ago, Jews were polytheistic, they believed in many gods. One of those gods was Yahweh, the other, El. Yahweh was the favored god of the southern region Judah, while El was primarily worshipped in the northern region Israel (hence the name Isra-EL). Well, after Israel was conquered by the Assyrians, the Yahwists of the south became dominant, and started becoming henotheistic, which led to a process of elimination which wasn't even finalized until after the return from exile. When the Judahites returned, they intermingled with the remaining Judahites and Israelites. They decided that they needed a national religion for their new nation and they began work on the completing the Torah and filling out the Tanakh. Since there were more Yahwists, they fused together El and Yahweh and made the latter the more recent God.
Now along comes Christianity, just as Judaism (from Judah) was getting settled. Christians were a fuse of messianic Judaism (a very extreme Judaistic sect) and hellenistic gnosticism. Lot's of different Christians group arose, and finally the one in Rome imposed its authority and standardized Christianity. Most other churches, including CoE and Coptic Church sort of refused it at first, but now they are full fledge orthodox. Fast forward 500 years, shortly after the standardisation of Christianity, and into the Arabian peninsula where certain gnostic Christians sects existed (and if you go north, still exist). Along comes Muhammed who adopts the Jewish and Christian God and declared the name to be Allah (but remember, if it were a true God, the name would far surpass any name a human could impose on it). In short, yes, Allah-Yahweh-El-Theos are the same gods.
As for the religious tensions, I might want to warn Jarvis (you look awfully familiar, Jarvis...TWeb?) that Protestant-Catholicism was one church during both the Crusades and inquisition. Protestantism is highly unfounded, taking the Bible to be the supreme authority, when it truth, Catholics compiled it! The Bible, though holy, was never supposed to be the final word, Paul gave that authority to the bishops, or elders. And even they looked directly to God. The Bible was merely an attempt to keep the orthodoxy since Marcion's gnostic sect had already adopted a canon, Luke + Paul - Judaism = Marcion's canon. But on to fightings, even today, Christianity is still doing damage, the Irish terrorists, fighting with Muslims in Africa, heck, even abortionist bombers in America. Every country you named has Christian terrorists also. Fanatics are dangerous period.
And yes, the Bible does support terrorism, if taken that way. Ever read Exodus? Then you would know that Moses ordered the deaths of every Hebrew who didn't want to follow the Lord MAN WOMAN AND CHILD! Even Jesus (which Jesus?) ordered the death of people (see Lk. 19:27). Regardless, any religion which condones the eternal torture of people is a wicked religion. You have no justification.