OK, I have read more Initially, it was not clear to me what Josiah had to do with Egyptians and Assyrians. Ignorance is not bliss! Thanks.
The whole scenario seems nonsensical to me. Why would Necho march all the way to the Euphrates, to help Assyria? Must be 500 miles. We’re offered no explanation at all, merely a bare-facts report. My inference is that Josiah’s territorial testosterone skyrocketed at Necho’s mere presence, which the text implies was altogether unrelated to Judah.