‘ And so it happened that after these things Joshua, the son of Nun, the Servant of YHWH, died, being a hundred and ten years old.'
Having accomplished his purpose, given by YHWH, of taking over from Moses and leading the people into the promised land, and then making it possible for each man to receive an inheritance in the land, Joshua died. He was given the title only specifically used by men of two people, Moses and Joshua. He was called ‘the Servant of YHWH'.
“After these things.” After what had been described in the book.
The age is approximate. Most ancient patriarchs who died were aged in round numbers. But one hundred and ten was the age of Joseph when he died (Genesis 50:22), and that in Egypt was considered to be the perfect length of life. In other words Joshua lived a full and complete life.
Moses died at one hundred and twenty. His life was split into approximately three periods of forty years. See Exodus 2:11; Exodus 7:7; Deuteronomy 29:5. As forty years represented a generation that really said that he had lived three full generations.