Did God force Pharaoh to sin?  Did God violate Pharaoh's free will?  Did God make Pharaoh hard?  How did God harden Pharaoh without attempting against his free will?

            "And the LORD said unto Moses: 'When thou goest to return into Egypt, see
        that thou do all those wonders before Pharaoh, which I have put in thine hand;
        but I will harden his heart, that he shall not let the people go.' " ( Ex 4: 21 )

    In this passage God says very clearly that He will harden Pharaoh's heart.  Do humans have free will?  Is this case an exception?  No, there was no exception in this case.  Pharaoh kept his free will all along this episode.  The explanation for all this seeming paradox is to realize what was the method God used to harden Pharaoh.  This case serves to demostrate that we should not set doctrines based on just a verse, a chapter, a passage or even a book of the Bible.  Our doctrines have to be in harmony with the whole teachings of Bible, not only a section of it.
    Let's imagine that Moses come before Pharaoh and said:  "God is going to strike lightning near you.  After that, you are going to suffer from a headache which will grow worse, and worse, and worse until you let the people leave". Let's suppose that the lightning strikes beside Pharaoh and that he started to suffer horribly from a growing headache.  How long do you think Pharaoh would refuse to let the people go?  Two hours, four hours, twelve hours?
    God could have used this method, but if He would have, Pharaoh would not have hardened is heart for more than a few hours; but this was not God's plan.  In this case it would not had made any sense to send the plagues, nor would it demonstrate the evil of Pharaoh.  It was necessary to send mild and time limited plagues to Pharaoh, so that he could get the wrong idea that God was weak and not very smart. That way Pharaoh would harden himself without God forcing his free will.  The same thing would have happened if God would have sent him an asthma attack that grew worse and worse every hour till he let the people go.
    When the first plague came, which was to convert the water into blood, it only lasted for seven days;  the Egyptians dug wells in a haste near the river, and were able to have access to drinkable water.  If God would have caused the water of the wells to become blood  and the plague to continue indefinitely, Pharaoh would have surrendered.  Even his generals, soldiers and the people, who were going to be dying of thirst with their children, would had forced him to let the people go.  Something similar happened in Ex 10: 7-8, where Pharaoh had to step down from his former position, because his servants were ready to start a mutiny.

            "And Pharaoh's servants said unto him: 'How long shall this man be a snare
        unto us? Let the men go that they may serve the LORD their God. Knowest thou
        not that Egypt is destroyed?' And Moses and Aaron were brought again unto
        Pharaoh, and he said unto them: 'Go, serve the LORD your God, but who are they
        that shall go?' "                                                                 ( Ex 10: 7-8 )

    Did God use a harsh, radical, strong, unbearable method to break Pharaoh down?  No, on the contrary, God used mild, short lasting, seemingly weak methods, which gave Pharaoh the foolish hope that he could deceive and overcome God.  Let's take a look at how God dealt with Pharaoh and the situation:

    a) Instead of ordering Pharaoh by means of lightnings, thunders and earthquakes to release the people, God, through Moses, asked him softly to let the people go. And what was Pharaoh's reaction? To grow haughtier and oppress the people even more.

            "And afterward Moses and Aaron went in, and told Pharaoh: 'Thus saith the
        LORD God of Israel: Let my people go, that they may hold a feast unto me in
        the wilderness'. And Pharaoh said: 'Who is the LORD that I should obey his
        voice to let Israel go? I know not the LORD, neither will I let Israel go'."
                                                                                                                ( Ex 5: 1-2)

            "And Pharaoh commanded the same day the taskmasters of the people, and
        their officers, saying: 'Ye shall no more give the people straw to make brick,
        as heretofore: let them go and gather straw for themselves. And the tale of the
        bricks,which they did make heretofore, ye shall lay upon them; ye shall not
        diminish ought thereof:  for they be idle; therefore they cry, saying, Let us go
        and sacrifice to our God'."                                                           ( Ex 5: 6-8 )

    After this order against God's plans, nothing happened to Pharaoh.  He probably thought that God was not powerful enough.  His thoughts could have been:  "I am Pharaoh; if someone dares to treat me with disdain as I have treated that God, I would have them crushed and grinded.  If that God was powerful He would have crushed me already, since He hasn't, he must not be powerful."
    b) What was God's next step?  It was not an action to demonstrate His power, but instead, something mild; something that He knew Egyptian magicians could imitate with their tricks, therefore allowing Pharaoh think that he had the same powers as God's representatives.

            "And the LORD spake unto Moses and unto Aaron, saying: When Pharaoh shall
        speak unto you, saying: 'Shew a miracle for you', then thou shalt say unto Aaron:
        'Take thy rod, and cast it before Pharaoh', and it shall become a serpent. And
        Moses and Aaron went in unto Pharaoh, and they did so as the LORD had
        commanded; and Aaron cast down his rod before Pharaoh, and before his servants,
        and it became a serpent. Then Pharaoh also called the wise men and the sorcerers:
       now the magicians of Egypt, they also did in like manner with their enchantments.
        For they cast down every man his rod, and they became serpents. But Aaron's rod
        swallowed up their rods. And He hardened Pharaoh's heart, that he hearkened not
        unto them; as the LORD had said."                                             ( Ex 7: 8-13 )

    No one can create matter, ( especially living creatures ) except God Himself.  Satan, demons and their representatives on Earth can not create matter, or a snake or any other living creature.  What these magicians did was the same thing that we see in theaters.  Have you ever seen a magician who cracks and drops two eggs into a hat and brings out two pigeons?  The Egyptian magicians were not going to tell Pharaoh that it was just a trick; they would make him believe that they created those snakes.   Pharaoh must have thought that he was not going to give up, because he had at his disposal almost the same power that Israelites' God had.  It is obvious that it was after this episode of the snakes that Pharaoh hardened his heart.  After each step, after each apparent victory he achieved, he hardened his heart.  God did not harden him, He just acted in such a way that Pharaoh, who was an evil person, could think that he could win after all, and overcome God.  It was enough to harden him.
    c) The third step was to turn their waters into blood  ( Ex 7:15-18 ).  When Pharaoh saw that his magicians did something similar, ( probably with dyes ), and especially when he saw that he could escape thirst, he hardened his heart again ( 7: 22 ).
    Nevertheless the miracle of Moses and the "miracle" of the magicians was not the same.  They  "changed" a vessel full of water into "blood",  rather into something that looked like it.  Moses changed the water of the Nile River and all ponds, into real blood, as God worked through Moses. Remember that the Nile River is the second or third largest in the world in volume of water.  It was meant to turn millions of tons of water into real blood for a week, and to kill millions of fish.
    d) Later came the frogs ( 8: 6 ).  The magicians with their tricks could bring more frogs, but they could not get rid of them.  The frogs were a real pain in the neck, so Pharaoh decided to humble himself a little and made a false covenant with Moses.  You get rid of the frogs, and I'll let you go. Once the plague was taken out Pharaoh would think like this:
    "Now who is going to force me to fulfill my word?  Let me back off to see what happens". Pharaoh did not let the people go, but the plague did not come back.  Pharaoh's thought was probably more or less the following: "This God is not very strong, because He could not bring back the plague.  He is not very smart either because He believed my lies, He did not ask for any warranty.  Besides I have noticed that He can not repeat the same plague, nor can He keep it for long.  After a while He will be out of plagues.  He cannot read my thoughts, because he believed my promise and did not know that I was not planning  to accomplish my promise.  I think I can overcome Him, and then, I will become a famous king  and in addition I will keep my invaluable slaves.  It is worth fighting for.  Maybe I can discover some other weakness in this God, and win Him over".
    Of course all these examples are hypothetical, but very close to what Pharaoh was probably actually thinking.  Every time that he hardened his heart it was because he felt he won an apparent victory.  When the magicians gave up ( Ex 8:19 ), Pharaoh already had thought he had won enough partial victories so as to believe he could fight and overcome God.  As a result of Pharaoh's so called victorious thoughts, he became more arrogant.
    God had harden Pharaoh's heart, but not by changing his personality or feelings, instead by allowing Pharaoh to have apparent victories, and as a result God not demonstrating all His power.
    It is easy to guess the sequence of the steps that led Pharaoh to harden his heart to the point of loosing his life in the Red Sea.  After the magicians collapsed, he tried again by deceiving" God by promising to let the people go as soon as the flies were taken away.  The flies were taken away, but Pharaoh refused again to let the Hebrews go.  When all the Egyptian cattle died, and Israelite's didn't, Pharaoh probably planned to confiscate Israelite's cattle as soon as he overcame God, or as soon as God  "became tired"  and  "left Egypt unto the place that He was before".  The other plagues probably followed the same pattern.
    God hardened Pharaoh's and the Egyptians' hearts to the point where they continued to follow God's people into the Red Sea.  God did it by ordering Moses to put the people in a dangerous position, and by making the Egyptians realize that the Israelites were cornered; and that they did not have Israelite servants anymore.

            " And the LORD spake unto Moses, saying:  'Speak unto the children of Israel,
        that they turn and encamp before Pihahiroth, between Migdol and the sea, over
        against Baalzephon, before it shall ye encamp by the sea'.  For Pharaoh will say
        of the children of Israel, 'They are entangled in the land, the wilderness hath
        shut them in.'  And I will harden Pharaoh's heart, that he shall follow after them;
        and I will be honoured upon Pharaoh, and upon all his host; that the Egyptians may
        know that I am the LORD. And they did so."                                ( Ex 14: 1- 4 )

            "And it was told the king of Egypt that the people fled; and the heart of Pharaoh
       and of his servants was turned against the people, and they said: 'Why have we
        done this, that we have let Israel go from serving us?  And he made ready his
        chariot, and took his people with him;  And he took six hundred chosen chariots,
        and all the chariots of Egypt, and captains over every one of them.  And the LORD
        hardened the heart of Pharaoh king of Egypt, and he pursued after the children of
        Israel: and the children of Israel went out with an high hand."         ( Ex 14: 5-8 )

    God does not take from us the free will which he gave us before.  It is evident that God does not go against what He established before, but in His wisdom uses various means to lead humans to accomplish His purposes.
    When God predestined Pharaoh for all these events, He did not predestined him to be evil, hard or arrogant.  He only predestined Pharaoh to be king of Egypt in the moment that the Israelites were to leave Egypt, as we are told in Ex 9:16.

            "And in very deed for this cause have I raised thee up, for to shew in thee
        my power; and that my name may be declared throughout all the earth." ( Ex 9:16 )

    God knows every soul He has created. He sent a soul to the body of the baby who was going to be born to the former pharaoh, a soul that He knew was going to become evil, hard and arrogant.  That way, when that baby became the king of Egypt, God could show His power to Israel and the world.  If that soul would had been sent to the body of a slave's son, that person was going to be evil, hard and arrogant anyway, but he could not execute evil against Moses.  It is evident that God predestines certain souls to some place, circumstances and time, in order to execute His will. God does not predestine a soul to be lost or saved, good or evil.
    In conclussion, it is good to take into consideration, that the magicians did not have any supernatural power as many brethren think.  Many brothers say that the magicians had satanic powers.  No, they didn't.  The only satanic "powers"  they had was the power to deceive.  They deceived their "public", in this case Pharaoh and his court.  If the magicians had any power, they would have protected Pharaoh from the frogs.  What I want to make very clear is that the Egyptian magicians ( Jannes and Jambres according to Paul in II Tim 3:8 ), did not have "satanic powers" as many naïve brothers think.  Even Satan does not have those creating  "powers".   The only satanic "power" that the magicians had was to know how to deceive others.  Nobody in this world has the power to create; only God has this power.