One way Joshua can be used is as tool for examining our own national origins. As citizens of a country with conquest and genocide as part of its history, Christians in the USA can use Joshua to help evaluate our nation's origins and history.
My colleague at Ashland Seminary, Professor L. Daniel Hawk, has been working on this topic for sometime now as reflected in his book Joshua in 3D: A Commentary on Biblical Conquest and Manifest Destiny (Cascade, 2011). His most recent publication on the topic is an article in Interpretation titled The Truth about Conquest: Joshua as History, Narrative and Scripture. Here is the abstract.
The Book of Joshua constitutes a vital biblical resource for interpreting modern narratives of conquest and colonialism. As a historical narrative, it reveals the fluid and complex character of national memory; as a national narrative of origins, it points to processes and motifs that shaped the identities of both Israel and the United States; as a scriptural narrative, it presents a revelatory vision that illumines contemporary narratives of conquest and evokes the stories of both colonizing and colonized peoples.
You can read that whole article online since Interpretation is allowing full access for a short period. I am unsure when it will go behind the subscription wall. In the mean time here is an excerpt.
The motifs and convictions that configure Joshua—God as founder of the nation and the divine warrior who fights for it; the conviction of set-apartness from other peoples; union via a common covenant; the contingency of national well-being on devotion and duty—comprise the basic building blocks of American national mythology. They derive from the typological hermeneutic of the Puritans, who saw themselves as the New Israel and read their emigration to the New World in light of the exodus: God delivering his people from oppression by a passage through water to the “New Canaan.” These motifs were taken up and transformed in the Revolutionary era by the Founding Fathers, who needed a centralizing genealogy to unite thirteen fractious colonies into a single nation. Biblical symbols and tropes channeled religious sentiment—the depth of feeling and devotion that characterized love of God—toward devotion to the nation—love of country. The Puritan sense of calling to preach liberty to the captives was transposed into a new key as a national mission to bring liberty and civilization to humanity. Puritan beliefs in God’s providential design and destiny found new expression in the conviction that America is uniquely destined by the inexorable progress of human history to be the harbinger of freedom and republican democracy. Combined with beliefs in the distinctive heritage and character of the Anglo-Saxon race, and reinforced in the nineteenth century by scientific racialism, these convictions fueled westward expansion and informed the narrative of Manifest Destiny that legitimized the growth of the American empire.
Do read it while you can. I think you will find Hawk provides some keen insights about Joshua and how the book can help us rethink our origins and history as a country.