Did Muhammad terrorize people to accept Islam?
When critics allege that people were, “terrorized into submission,” they cite a verse in the Qur’an, 8:13. The verse in question states, “When thy Lord revealed to the angels, saying, ‘I am with you; so give firmness to those who believe. I will cast terror into the hearts of those who disbelieve. Smite, then, the upper parts of their necks, and smite off all finger-tips.’” 
In this verse, God is relating the story of Badr—the battle that Muslims fought in self-defense against the invading Meccan army.
In the Battle of Badr, a woefully ill trained and outmatched army of 313 Muslim men and children defended their right to practice their faith peacefully against a well-trained and well-equipped army of 1,000 Meccan soldiers. In fact, many of the Muslims fought in self-defense with sticks and wooden swords—terrifying isn’t it? In verse 8:13, God reminds the Muslims that their victory was as a result of His Divine help with angels and not their own doing. Nothing in this verse indicates, suggests, or commands terror into the hearts of those who do not submit to Islam. Instead, it refers to God’s response to those who persecuted Muslims relentlessly in Mecca for 13 years, and even now pursued Muslims a month’s journey to Medina to murder them.
 Qur’an 8:13.