וַיֵּצֵא֩ סִיחֹ֨ן לִקְרָאתֵ֜נוּ ה֧וּא וְכָל־עַמּ֛וֹ לַמִּלְחָמָ֖ה יָֽהְצָה׃
At lumabas si Sihon laban sa amin, siya at ang kanyang buong bayan, upang makipagdigma sa Jahaz.
Rashi
ויצא סיחן AND SIHON WENT FORTH — He did not send for Og to help him: this serves to teach you that they did not require one another's help, so mighty was each of them.
Siftei Chakhamim
He did not send for Og, etc. Because they were powerful.