Today's reading is Joshua 5-8 (read it in the KJV or NIV)
Today's passage covers the Israelites' circumcision at Gilgal; the fall of Jericho; the routing of the Israelites by the men of Ai because of Achan's transgression; the ambush and destruction of Ai; and the renewal of the covenant.
Despite the Israelites' fierce military reputation, their first few battles show them to be actually quite cowardly.
In today's readings, we have three military encounters: first at Jericho (Josh. 5:13-6:27), second at Ai (Josh. 7:2-9), and third again at Ai (Josh. 8:1-29). In each of them, the Israelites' performance as hardy warriors seems to be lacking.
Everyone knows the story of the walls of Jericho: Joshua circled the city for seven days, and then the walls of Jericho came "crumbling down" (as the song says). This is, for the most part, true. For six days, the warriors of Israel circle Jericho, followed by the ark of the covenant and priests blowing trumpets. On the seventh day, they circle seven times, the warriors shout, and the walls fall down.
And then the Israelites kill every man, woman, and child, along with all the cattle, and burn the city to the ground. (Josh. 6:21-24) In fact, it seems like the men of Jericho never had a chance: the Israelite conquest wasn't so much a victory as a slaughter.
Next comes the city of Ai. Unbeknownst to the Israelites, one of their number, Achan, took some forbidden spoils from Jericho and turned God away from his chosen people. So when the Israelites send 3,000 men to storm Ai, they are routed. In fact, the text tells us that "about 36" Israelite warriors fell before the forces of Ai. (Josh. 7:5) Because of this supposedly horrible catastrophe, Joshua goes into full mourning, asking God why he has abandoned the Israelites. (Josh. 7:6-9)
In the end, Achan is discovered, forced into confession, and stoned. (Josh. 7:16-26) That out of the way, the actual conquest of Ai can proceed.
This time, Joshua is taking no chances. Not only does he send a force of 30,000 men against Ai's total population of 12,000, (Josh. 8:25) he also makes sure that strategy is on his side as well. Knowing that the men of Ai would hunt down the Israelites after their last victory, Joshua sends a force of 30,000 men (or possibly 5,000 men, depending on whether you believe Josh. 8:4 or 8:12) to wait in ambush until the men of Ai leave to follow the remaining Israelites. Then the men lying in wait are to seize the city and burn it to the ground.
This is exactly what happens. By the time the men of Ai realize their city is on fire, Joshua's forces have turned around and confronted them head-on. The men of Ai are caught between Joshua's pretended rout and the main force of the ambush. Joshua then proceeds to kill all the fighting men, as well as the rest of the population of the city. They burn Ai to the ground, hang its king, and leave him at the gate of his ruined city. (Josh. 8:20-29)
Let us take stock of these first three Israelite battles. The first thing we learn is that not many Israelites died. In fact, it seems like the sum total of the deaths are the "about thirty-six" who fell during the first attack on Ai. We don't read about any other deaths, either during the attack of Jericho or the second attack on Ai. While it's certainly possible that some of the Israelite soldiers died in the attacks, it is equally possible that, because of God's protection, they didn't.
On the other hand, the Israelites were extremely brutal with their victims: at both Jericho and Ai they burned the cities to the ground, killed all the inhabitants (not just the soldiers), and even gave orders against ever rebuilding the cities again. God commanded them only to take the gold, silver, brass, and iron -- for God's treasury -- and to destroy everything else at Jericho. (Josh. 6:18-19) At Ai, they were also allowed to take the livestock. (Josh. 8:27) Otherwise, everything was "utterly destroyed."
We have to wonder about the Israelites' tactics. On the one hand, they were certainly continuing their reputation as savage conquerers, barbaric even beyond the barbaric standards of the time. When their enemies heard that the Israelites were coming, they likely started quaking. On the other hand, this is hardly a way to settle comfortably among your new neighbours. Yes, God was going to give the entire land to the Israelites, making "neighbours" somewhat irrelevant. But there would still be neighbours beyond the Israelites' borders, whom they would need to interact with.
One final thought: much later, the Israelites lament when their land is attacked by nation after nation. The Assyrians, Babylonians, and Persians all successively attack and conquer portions of the Israelite lands, killing some of their men and sending the rest into exile. This is one of the laments of Jewish history, in fact. On the other hand, even these conquering nations seem not to have been as brutal as the Israelites themselves were when they first conquered the lands in these chapters. As the saying goes, "those who live by the sword, die by the sword."