The three religions trace their origins back to Abraham, who, in Genesis, had humanity's first relationship with God after the failures of Noah's flood and the Tower of Babel. Judaism and Christianity trace their tie to Abraham through his son Isaac, and Islam traces it through his son Ishmael.
The different branches of the government help limit the power of the federal government because there are checks and balances with each branch and if one branch doesn't quite agree with the executive branch then the two other branches can overrule the president's power.
