After Muhammad's death, Muslims needed someone to rule according to their holy book, the Qu'ran. It divided the Muslims because of their disagreement on who they thought would be an ideal leader (caliph). Sunni's believed that any Muslim most capable of ruling should be able to rule, but the Shia believed that a Muslim leader would need to be a descendant from Muhammad and related in some way.
That the religion and race will have fights about who is true
Answer:
Led to higher casualty rates
Made it a defensive war
Defenses against chemical weapons were required
Explanation:
It did lengthen the fighting time, but it wouldn't make sense if casualties were lessened. WWI did not last for a short time, so your only options are above this text.
