The opening lines of Yonah, written here, pose a serious yet oft-overlooked question: Why did Yonah run away from Hashem's command?
Answer #1: Yonah was in favor of strict judgement, and didn't want G-d to be merciful on sinners.
Yeah, no. You see, Bnei Yisrael were also egregious siners, and yet Yonah was fine prophesying the military victory of Israel, which is clearly described as an action sanctioned by G-d out of pity.
In the style of the Gemara, I will use this opportunity to go on a completely unconnected tangent. A commonly noted thing about Yonah is that there is virtually no introduction to our protagonist. However, this is untrue; the Tanach merely assumes that you already know Sefer Melachim, where you learn Yonah's political affiliation (Pro-Israel), his hometown (Gat Chepher), and his personal description (Eved Hashem).
Answer #2: Assyria was a foe of Israel, and Yonah wanted them destroyed.
This answer seems compatible with our description of Yonah, but actually displays a sad lack of knowledge concerning the political realities of the 9th-8th centuries' Middle East. Here's a picture:
In this picture, we see Israel paying tribute to Assyria in exchange for an alliance against Aram. Assyria, during Yonah's time, would attack Aram, providing relief for Israel. Thus, it would be in Israel's best interest to save Nineveh.
While I cannot offer my own satisfactory opinion, there is a midrash that picks up on the need for a good theory.
פרקי דרבי אליעזר: פרק עשירי
ולמה ברח? אלא, פעם ראשונה שלחו להשיב את גבול ישראל ועמדו דבריו. פעם שניה שלחו לירושלים להחריבה. כיון שעשו תשובה, עשה הקב"ה כרוב חסדו ונחם על הרעה ולא חרבה, והיו ישראל קורין אותו נביא שקר. פעם שלישי שלחו לנינוה. דן יונה דין בינו לבין עצמו. אמר, יודע אני שזה גוי קרובי תשובה הם. עכשיו עושין תשובה, והקב"ה שולח את רוגזו על ישראל. ולא די שישראל קורין אותי נביא שקר, אלא אף עכו"ם!?
Pirkei D'Rabbi Eliezer 10
Why did he flee ? Because on the first occasion when (God) sent him to restore the border of Israel, his words were fulfilled, as it is said, " And he restored the border of Israel from the entering in of Hamath " (2 Kings xiv. 25). On the second occasion (God) sent him to Jerusalem to (prophesy that He would) destroy it. But as soon as they repented, the Holy One, blessed be He, did according to the abundance of His tender mercy and re- pented of the evil (decree), and He did not destroy it ; thereupon Israel called him a lying prophet. On the third occasion (God) sent him against Nineveh to destroy it. Jonah argued with himself, saying, I know that the nations are nigh to repentance, now they will repent and the Holy One, blessed be He, will direct His anger against Israel. And is it not enough for me that Israel should call me a lying prophet ; but shall also the nations of the world (do likewise) !?
While this midrash is certainly not peshat, it does solve our problem.
Tune in for installment #2 of my Yonah series, coming soon!