Unfortunately, Islam has heavily borrowed from Judaism and Christianity. Other proofs that Islam is not really an authentic religion is that Gabriel only appeared to Mohammed. There were no other witnesses who can corroborate what Mohammed claims he saw and heard. This is very akin to Mormonism that is prevalent in the United States and a rapidly growing international religion.
Now internal flaws of the Quran include referring to Jesus as a prophet and not a Son of God. If Jesus was a God ordained prophet, then why would he lie? If he was telling a lie, the prophet Mohammed can be a liar too. If Jesus was not lying then Mohammed is still a liar.
It must be understood that Mohammed was involved in warfare and that's how he captured Mecca - and not at the first attempt.
