Who are the many nations that Abraham was called by God, 'the father' of? Who are these nations that Abraham was father of, according to God's words?

Gen 17:5 (NIV)


  5 No longer will you be called Abram[a]; your name will be
  Abraham,[b] for I have made you a father of many nations.
  
  Footnotes:
  a. Abram means exalted father.
  b. Abraham probably means father of many.
As you can see; from this Patriarch lineage depiction taken from the book of Genesis, Abraham was indeed the father of many Nations.

There are some Things worthy of notice which many are not aware of:

Abram had a second wife named Keturah and had six sons by her, and possibly daughters.

Rebecca was Isaac's cousin.

Basemath/Mahalth was Esau's cousin.


Not shown on this chart are some facts which are cogent to your question that are available in other records of that Era.

The Ishmaelites are the predecessors of the Bedouin tribes.

The Edomites and the descendants of Abraham through Keturah, are the Arabic Nations.



( it is the opinion of some that the line through Keturah is the Palestinians, but there are apparently no known records to verify that claim).


The animosity between the Arabic Nations and Israel stems from:


Genesis 25:29 through 34  And Jacob sod pottage: and Esau came from the field, and he was faint: 30  And Esau said to Jacob, Feed me, I pray thee, with that same red pottage; for I am faint: therefore was his name called Edom. 31  And Jacob said, Sell me this day thy birthright. 32  And Esau said, Behold, I am at the point to die: and what profit shall this birthright do to me? 33  And Jacob said, Swear to me this day; and he sware unto him: and he sold his birthright unto Jacob. 34  Then Jacob gave Esau bread and pottage of lentiles; and he did eat and drink, and rose up, and went his way: thus Esau despised his birthright.

The point of contention is that Jacob stole Esau's birthright and that the land all belonged to Esau as the firstborn son.