In truth, I do not think that the book of Joshua portrays God as a murderer as much as many conclude. My opinion is based on a perspective of biblical studies, archaeology, and linguistics. Please allow me to explain more.
Many would cite Josh. 6:21 "They devoted the city to the LORD and destroyed with the sword every living thing in it—men and women, young and old, cattle, sheep and donkeys."
Is this an act of genocide - or at least of murder - on God's part? Several areas need consideration before coming to a conclusion.
Firstly, let us consider the phrase "men and women." The phrase in Hebrew is me'ish ve'ad 'isha, (lit., from man and unto woman) and appears multiple times in the Hebrew Bible. When considering the meaning of a phrase or word, one of the most basic steps is to observe how it is used in multiple contexts. The phrase from man and unto woman appears in contexts where no woman would have been present. Consider Ai of which the phrase is used again. Ai is a known fortress - only soldiers would have been present - no women and no children would have been in the fort.
Then we can conclude that the phrase "men and women" in Hebrew does not necessarily denote the actual presence of both men and women. Rather, the phrase is a way to indicate "all who were present."
Secondly, let us consider archaeology. The biblical site of Jericho from Joshua 6 is very disputed. However, there is at least the potential for the site to be a military fort (rather than what we traditionally translate as a "city.") The model of a military fort would not only fit the biblical story very well, but the archaeological evidence may support this as well. Additionally, the word in Hebrew used to describe Jericho (and other sites that Joshua attacked) is 'ir. The word can justly be translated "city," but it can also mean "town," "village," and "fort."
While the theory is admittedly somewhat hypothetical in nature - I find it likely that Joshua was not attacking a city and murdering men and women. Rather, Joshua and Israel were commanded to attack a military fort, and they put to death all of the soldiers who opposed them.
This leaves more questions unanswered (i.e., How can God wage war?), but Joshua does not necessarily portray God as a cruel and unjust murderer who commanded Israel to destroy children and women.