Pharaoh-Nechoh - This king is well known to us both from profane historians, and from the Egyptian monuments. He succeeded his father Psammetichus (Psamatik) in the year 610 B.C., and was king of Egypt for 16 years. He was an enlightened and enterprising monarch. The great expedition here mentioned was an attempt to detach from the newly-formed Babylonian empire the important tract of country extending from Egypt to the Euphrates at Carchemish. Calculating probably on the friendship or neutrality of most of the native powers, the Egyptian monarch, having made preparations for the space of two years, set out on his march, probably following the (usual) coast route through Philistia and Sharon, from thence intending to cross by Megiddo into the Jezreel (Esdraelon) plain.
The king of Assyria - This expression does not imply that Nineveh had not yet fallen. The Jews, accustomed to Assyrian monarchs, who held their courts alternately at Nineveh and Babylon 2 Kings 19:36; 2 Chronicles 33:11, at first regarded the change as merely dynastic, and transferred to the new king, Nabopolassar, the title which they had been accustomed to give to their former suzerains. When, later on, Nebuchadnezzar invaded their country they found that he did not call himself “King of Assyria,” but “King of Babylon,” and thenceforth that title came into use; but the annalist who wrote the life of Josiah inmediately upon his death, and whom the author of Kings copied, used, not unnaturally, the more familiar, though less correct, designation.
Josiah went against him - Josiah probably regarded himself as in duty bound to oppose the march of a hostile force through his territory to attack his suzerain. For further details see the account in Chronicles (marginal reference). On Megiddo, see Joshua 12:21 note.