Why does the Torah use the word "Vaya'al" in connection with Yisrael's moving towards Og Melech ha'Bashan?
Rashi: Whenever one travels northwards, it is considered an ascent.
Why did Moshe not sent a message of peace to Og, like he did to Sichon?
Ramban (on 2:34): Because Og attacked Yisrael before he had a chance to do so.
Rosh (2:26): Most of Sichon's land was initially from Amon and Mo'av. Og's land was Eretz Refa'im (which was promised to Avraham), so he did not send for Shalom, for we do not call to the [Da'as Zekenim, Hadar Zekenim (2:26) - seven] nations for Shalom. 1
The Yerushalmi (Shevi'is 6:1) and Vayikra Rabah (17:6) say that Yehoshua did send offers of Shalom to the Kena'ani nations! (PF)