In times of war in the Book of Mormon it seems quite odd that a whole group of able-bodied men would be granted exemption from taking up arms. This is contrary to ancient traditions in which all able-bodied men would be considered part of the army.
However there are several points which make the exemption of the Ammonites consistent with Jewish law:
How would Joseph Smith know requirements for military exemption and make this part of the storyline consistent with ancient Israelite law?
See: