1)
What is "l'Za'avah"?
1.
Rashi: This is like "Lo Kam v'Lo Za" (Esther 5:9). Similarly, Ga'avah is from the root "Ga Me'od" (Yeshayah 16:6). Anyone who hears the evil that comes on them, he is shocked.
2)
Why is it written l'Zava'ah, and we pronounce it "l'Za'avah"?
1.
Radak: They are different roots, but both of them refer to motion.
3)
Why is this attributed to Menasheh?
1.
Radak: He conducted Yisrael with evil deeds, and spilled innocent blood until Yerushalayim was filled with dead bodies, like it says (Melachim II, 21:16).
2.
Radak citing Targum Yonasan: For they did not repent, like Menasheh [repented].
3.
Malbim: The decree began in his days. Refer to Melachim II, 21:15:1:1.