As with other prophets, the "word of the Lord" came to him (Jon 1:1).  But this word was not for the people of Israel, but for Nineveh in Assyria, a city nearly 500 miles away.  God told Jonah to leave Israel and travel to Nineveh and preach against that city. Jonah's response to God's command was to run away from the Lord and take a ship for Tarshish.  The precise location of this city has been fodder for the arguments of generations of Biblical pedants.  It really doesn't matter where it was -- what mattered to Jonah was that it was anywhere but Nineveh.  The Bible tells us that he fled from the Lord (Jon 1:3).  The reason -- that he wanted Israel's potential enemies to perish -- is disclosed to us later in the book.  At first we only know that he was disobeying God.

         

At this time, the main enemy of Israel was Aram, just to the north.  In fact, Aram was a buffer between Israel and Assyria.  Later, Assyria would expand westward and crush first Aram and then Israel.  But this was about 50 years after Jonah's message.

        

The point is that God took notice of, and had a message for, a Gentile nation far away from Israel.  While other prophets frequently proclaimed the judgments of God on foreign nations, Jonah was actually sent to one of these nations to deliver the message in person. This makes the Book of Jonah unique among the prophetic books.