The book of Joshua is named from Joshua the son of Nun who
is the principal character in it.
Joshua had been a captain of Israel's army (Exodus
17:9-10) and a personal servant of Moses (Exodus
24:13). After the death of Moses, God chose Joshua to
lead the Israelites into the Promised Land.
Even before the land was completely conquered it was divided
up between the 12 tribes of Israel. The Levites and priests
were given 48 cities in different parts of the land and 6
cities were specially appointed as "cities of refuge"
where someone who had killed someone else accidentally could
flee to safety.
Jericho was the first city to be overthrown; Ai was the second.
They were followed by the cities of the south and then the
cities of the north. The conquest of Canaan was to be with
God's help and Israel had to trust Him.
[The name Joshua is very like Jesus - both
mean 'God saves'.]