1. (Religious answer) Because Abraham wouldn't worship false idols with his nephew, so he and his wife Sarah, left to settle in a different land which happened to be in the fertile crescent.
2. Because being close to the rivers and the floods made good farm land. <span />
If a bill has passed in both the U.S. House of Representatives and the U.S. Senate and has been approved by the President, or if a presidential veto has been overridden, the bill becomes a law and is enforced by the government.