I think it will be "other" in two possibilities, ranked below in order of greatest probability:
1.) Supply Disruption - While this would likely result in civil unrest and/or economic collapse, the cause will, I think be primarily a disruption. This could be either due to a mass shortage of something essential (corn or wheat) or a major disruption of fuel, causing our modern distribution center model of grocery to fail due to costs. A heavy enough disruption that lasts for even as short of a time as a month would create havoc as most people don't keep that much food on hand.
2.) Terrorism - I'm not talking about the actual actions, but the reaction causing a vast divide between the "security" minded and the "freedom" minded, causing a civil war.