Because Ishmael doesn't play by the conventional war rules. Now America just calls it a war on Terror. And this war is waged against everyone in the Middle East like it says in the scriptures about Ishmael.
When it says "AND HE SHALL DWELL IN THE PRESENCE OF ALL HIS BRETHREN." That is letting you know where the location of his people would be. Which is the Middle East. Mainly Saudi Arabia.)
Genesis 17:15 (KJV)
15 And God said unto Abraham, As for Sarai thy wife, thou shalt not call her name Sarai, but Sarah shall her name be.
16 And I will bless her, and give thee a son also of her: yea, I will bless her, and she shall be a mother of nations; kings of people shall be of her.
17 Then Abraham fell upon his face, and laughed, and said in his heart, Shall a child be born unto him that is an hundred years old? and shall Sarah, that is ninety years old, bear?
18 And Abraham said unto God,-O THAT ISHMAEL MIGHT LIVE BEFORE THEE!-
(Abraham did not understand the plans of the Most High. Abraham thought that the covenant would automatically be given to Ishmael because he is his firstborn son. Plus at this time he is 100 yrs old and his wife Sarah is 90 so he didn't expect to have anymore children.)
19 And God said, Sarah thy wife shall bear thee a son indeed; and thou shalt call his name -ISAAC: AND I WILL ESTABLISH MY COVENANT WITH HIM-for an everlasting covenant, and with his -SEED-after him.
(Here is where things get serious. Instead of Ishmael receiving the covenant. Remember God said he would be the God of the heirs of the covenant and he would give the heirs of the covenant the land of Canaan.
God is CLEARLY stating that his covenant would be passed down through Issac which was the second born son of Abraham by Sarah. And NOT Ishmael.)
20 And as for -ISHMAEL,- I have heard thee: Behold, I have blessed him, -AND WILL MAKE HIM FRUITFUL, AND WILL MULTIPLY HIM EXCEEDINGLY;-twelve princes shall he beget, -AND I WILL MAKE HIM A GREAT NATION-
(This is why you see Arab nations so wealthy today. God came through on his promise. We can't even imagine the level of wealth that God had blessed the son's of Ishmael with.)
21-BUT MY COVENANT WILL I ESTABLISH WITH ISAAC,- which Sarah shall bear unto thee at this set time in the next year.
1 And the Lord visited Sarah as he had said, and the Lord did unto Sarah as he had spoken.
2 For Sarah conceived, and bare Abraham a son in his old age, at the set time of which God had spoken to him.
3 And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac.
8 And the child grew, and was weaned: and Abraham made a great feast the same day that Isaac was weaned.
9 And Sarah saw the son of Hagar the Egyptian, which she had born unto Abraham, --MOCKING-
10 Wherefore she said unto Abraham, -CAST OUT THIS BONDWOMAN AND HER SON: FOR THE SON OF THIS BONDWOMAN SHALL NOT BE HEIR WITH MY SON, EVEN WITH ISAAC.-
11 And the thing was very grievous in Abraham's sight because of his son.
(The reason this was grievous to Abraham is because Abraham had grown attached to Ishmael. He was his firstborn.
Abraham did not understand what the Angel had told Hagar. And what had to come to pass.)