Quran (8:12) - "(Remember) when your Lord inspired the angels... "I will cast terror into the hearts of those who disbelieve. Therefore strike off their heads and strike off every fingertip of them" No reasonable person would interpret this to mean a spiritual struggle, given that it both followed and preceded confrontations in which non-Muslims were killed by Muslims. The targets of violence are "those who disbelieve" - further defined in the next verse (13) as those who "defy and disobey Allah." Nothing is said about self-defense. In fact, the verses in sura 8 were narrated shortly after a battle provoked by Muhammad, who had been trying to attack a lightly-armed caravan to steal goods belonging to other people. (See also: Response to Apologists)
Quran (8:15) - "O ye who believe! When ye meet those who disbelieve in battle, turn not your backs to them. (16)Whoso on that day turneth his back to them, unless maneuvering for battle or intent to join a company, he truly hath incurred wrath from Allah, and his habitation will be hell, a hapless journey's end."
Quran (8:39) - "And fight with them until there is no more fitna (disorder, unbelief) and religion is all for Allah" Some translations interpret "fitna" as "persecution", but the traditional understanding of this word is not supported by the historical context (See notes for 2:193). The Meccans were simply refusing Muhammad access to their city during the pilgrimage. Other Muslims were allowed to travel there - but not as an armed group, since Muhammad had declared war on Mecca prior to his eviction. The Meccans were also acting in defense of their religion, as it was Muhammad's intention to destroy their idols and establish Islam by force (which he later did). Hence the critical part of this verse is to fight until "religion is only for Allah", meaning that the true justification of violence was the unbelief of the opposition. According to the Sira (Ibn Ishaq/Hisham 324) Muhammad further explains that "Allah must have no rivals." (See also: Response to Apologists)
Quran (8:57) - "If thou comest on them in the war, deal with them so as to strike fear in those who are behind them, that haply they may remember."
Quran (8:67) - "It is not for a Prophet that he should have prisoners of war until he had made a great slaughter in the land..."
Quran (8:59-60) - "And let not those who disbelieve suppose that they can outstrip (Allah's Purpose). Lo! they cannot escape. Make ready for them all thou canst of (armed) force and of horses tethered, that thereby ye may dismay the enemy of Allah and your enemy." As Ibn Kathir puts it in his tafsir on this passage, "Allah commands Muslims to prepare for war against disbelievers, as much as possible, according to affordability and availability." (See also: Response to Apologists)