דברי הימים ב, פרק כ״ה, פסוק ו׳

Believing that he lacks a sufficient number of warriors, the king decides to fill the gap in his ranks by relying on an outside force. He reaches out to the neighboring Kingdom of Israel and hires one hundred thousand of their soldiers. Turning to this specific neighbor is a practical choice, as the Kingdom of Israel was a significantly larger nation than his own kingdom, allowing them to easily provide such a massive number of extra troops [ביאור שטיינזלץ].