And this [is] the cause why Joshua did circumcise
 Or the reason of the command given him to circumcise the children of Israel at this time, namely, what follows: 
 all the people that came out of Egypt [that were] males, [even] all
 the men of war;
 meaning such that were twenty years old, and upwards: 
 died in the wilderness, by the way, after they came out of Egypt;
 not directly, but in a course of forty years, as they journeyed through the wilderness; this is to be understood with an exception of Joshua, Caleb, Eleazar but then there was a large number who were under twenty years of age, that came out of Egypt, and were now living. 
The Brenton translation of the Septuagint is in the public domain.