Has anyone ever wondered why God closed Sara's womb until AFTER Ishmael was a young man?

We are told in the Bible that God promised Abraham that his seed would bless all the nations of the earth. But Sara, his wife, was barren.
Eventually, Sara agreed to give Abraham her slave girl, Hagar, saying "perhaps I can have children through her" (any child born to Sara's slave would be Sara's property.)
Later, when Hagar's son, Ishmael was about thirteen, we are told that Sara conceived and gave birth to a son, Isaac. Evidently, Ishmael thought that the sight of such an old woman nursing a child was rather funny, and he made some rude comment where the old lady could overhear. She insisted that Abraham throw out "this slave woman and her son", and, sadly, Abraham told God about it. God told him to "hearken unto the voice of thy wife"...so the old man threw them out of his camp.
The resulting history between the Arabs and the Jews has been a long, bloody struggle throughout their history, leading to the events we see unfolding around us today.
Did God plan it this way?
Why?

I'm interested in hearing what people think about this, no matter what religion you are.
Please be courteous in your answer, and remember that not everyone believes/thinks as you do.

Of course God planned it this way! :) He knows everything, from the very moment of Creation, He's been orchestrating history. Sarah disobeyed God by sending Hagar in to Abraham. Her disobedience cost the Arabs and Jews their peace. Sin has consequences. Those were the consequences.

Why did God plan it this way? Perhaps to show us that when we try to order things our way, they don't work out nearly as well as His way. ;)

God loves a good conflict and is continually seen setting them up in the bible.

He is like a 14 year old boy with an ant farm and a magnifying glass.

You have a very good question.I am puzzled too.I am sure God planned all of this but I do not know why.Why does God choose one person and not the other? Examples; Cain and Able,Ishmael and Isaac,Esau and Jacob,David rather than his brothers? This is one of my biggest questions.Abraham had 6 other sons after Isaac with Keturah.Maybe he had daughters as well,we are not told about.The Medianites and Amelekites were a curse to Israel but they also were Abraham's descendants.

I dunno, it seems like most of the ladies I am interested in close their womb pretty quickly when I show up...