Chapter 20

At the time Sargon sends an invasion to Ashdod - a major Philistine city - under his military commander instead of going himself, Isaiah is instructed by God to walk barefoot and naked as a portent of the coming destruction of Cush and Egypt.  He walked around this way for three years!  The footnotes say probably Nubia.  Assyria will conquer them, and march home the captives, naked and barefoot.  Then the northern kingdom, which has appealed to, or at least counted on and hoped that Egypt and Cush will help them and deliver them from the Assyrian invasion will understand that no help will come from there.  And for Israel, their hope of avoiding Assyrian invasion will be gone.  So it is safe to say that the events in Chapter 20 happened leading up to the Assyrian conquest of the Northern Kingdom.  This part must be past.  So that alliance spoken of at the end of Chapter 19 must be yet future.