I SAW in the Religion feature, dated 2nd December 2001, a letter to the Editor by a O.J. Cunningham; the page dealt with Islam and Christianity. I want to go into this topic, too, going even further back than the actual start of either religion; to the very beginning, to Genesis.
Christianity is rooted in God's former true religion, Judaism (Jewish religion). Abraham was the father of God's original chosen people, the Jews (now modern Israelis). In the book of Genesis we read where God promised Abraham in Genesis that a son he would bear by his wife, Sarah, would be his heir, the father of a great nation that would be a blessing to all nations (Genesis 12:2,3; 17:6, 18:18 - see also Isaiah 56). (This blessing would come through Jesus Christ's birth, ministry and teaching, death for our sins, and resurrection.)
Because both Abraham and Sarah were old, they began to doubt God when time passed without any son being born. Sarah convinced Abraham to follow a custom of those days, where the husband would take his wife's servant as a second wife if his wife was barren (Genesis 16:1-4).
Hagar, the servant began to "lord it over" Sarah when she was pregnant because Sarah was barren, and Sarah rebuked her - Hagar ran away (Genesis 16:4-6). (God had made only one Adam and only one Eve, after all - to try to do otherwise is to guarantee trouble). God told her, when she was alone in the wilderness, that her son, though not the heir, would also be a great nation (the Arabs, today), and that she should return to her mistress. He also told her that her son, Ishmael, and Sarah's son, Isaac, (and their descendants, Arabs and Israelis, today), would always be enemies, and that Ishmael and his descendants would be at war with all other nations, and would live in the same area as his brethren (the Israelis) (Genesis 16:7-16).
Christianity grew out of the Jewish religion, and would not have been separated from Judaism if the Jews had not rejected Jesus, the Son of God, of whom their prophets had foretold repeatedly throughout the Old Testament.
Christians who toss out the Old Testament are trying to stand on one leg instead of two). Now the Christian church has replaced the Jews (Isaac's descendants) as God's chosen people (Galatians 3:26-29; Hebrews 8:6-13; Jeremiah 31:31-34; Isaiah 59:21; Exodus 19:8; Matthew 21:33-46; Acts 7:51-53; John 4:21-26; Deuteronomy 18:15, 18-22; John 14:29; Hebrews 10:16,17; Genesis 12: 1-5, 17:7-14, 19, 21, 23-27; Hebrews 11 (especially verses 1, 6, 8-19, 32-40), Hebrews 12:1-3, 18-29;) and the Arabs (Muslims/Islamic people - the nation of Mohammed's origin), Ishmael's descendants, continue to fight them and the Israelis, as their ancestors fought the ancient Israelites in Bible times.
According to what God said in Genesis, this will continue until the end of this age (until Jesus come back to this earth to claim His faithful people and put an end to Satan's rule Genesis 1:28; John 12:31; Job 1:6,7, 2:1,2,). I hope this will be enlightening.