‘ And I sent the hornet before you, who drove them out from before you, even the two kings of the Amorites, not with your sword, nor with your bow.'
The ‘two kings of the Amorites' may be specific, or the word ‘two' may be used as meaning ‘a few' as it often does. Compare the ‘two sticks' of the widow of Zarepath (1 Kings 17:12). These were probably not Sihon and Og but two (or ‘a few') kings whom they were called on to fight on the west side of the Jordan. We do not know which ones. (‘Amorites' rather than ‘Canaanites' is found throughout the speech - Joshua 24:15; Joshua 24:18). Perhaps there is in mind here some striking incident that the people would remember. The point is made that it was achieved without fighting. (LXX has twelve kings but that was probably to remove the seeming difficulty caused by assuming that the two kings were Og and Sihon when such use of numbers was forgotten. But there were a number of kings of the Amorites, and as mentioned above the Canaanites were called Amorites throughout the speech - Joshua 24:15; Joshua 24:18, with those Beyond Jordan eastward being specifically distinguished - Joshua 24:8).
Whether this was a literal attack of hornets on the leaders of an Amorite army that caused them to have to flee, possibly forcing them out of ambush when a hornets' nest was disturbed, or an attack by insects on their chariot horses which panicked them and had a similar effect, or some other factor that accomplished the same, we will never know. But the reference to sword and bow is from Genesis 48:22. However, the point here is that Israel were more favoured for they did not need sword or bow.
The reference to hornets recalls Exodus 23:28; Deuteronomy 7:20. It does not mean that the hornets literally went in front of the Israelite army, but that God had prepared them to do this work beforehand. These two references probably have in mind the hornet of fear and anxiety (Exodus 23:27-28) caused by hearing stories of what YHWH had done for Israel, but Joshua here may well have associated them with a particular striking incident of help gained from swarms of insects. Some have connected sir‘ah (hornet) with Assyrian siru (serpent) and have associated it with the sacred serpent on the crown of Pharaoh, with the idea that a preceding Egyptian invasion had prepared the way for Israel's successes, but this seems less likely. However the meaning of sir‘ah is not certain for it appears only in these contexts.
Some do see it as referring to the Og and Sihon, who are elsewhere called ‘two kings of the Amorites' (Joshua 2:10; Joshua 9:10; Deuteronomy 3:8; Deuteronomy 4:47), recognising that they might have come into his mind as a result of his mention of Amorites, and that the emphasis here is on the hornet YHWH sent rather than on the kings, with YHWH seeing them as simply part of the whole campaign.