100. Did the Prophet Muhammad fight only in self-defense? What led to the Battle of Khandaq (the Battle of the Trench)?

All skirmishes that we see in the life of the Prophet were in self-defense. None was done as offensive action directed against others.

The Battle of the Trench happened in 627 AD. When the Prophet came to know that people were coming from Makkah to attack the Muslims of Madinah, he gathered all of his Companions and asked them how to deal with the situation in a non-confrontational manner. One of them, Salman Farsi who was from Persia, said that in Iran whenever kings have to avoid a battle, they dig a trench around their area. The Prophet liked this idea and all of the Muslims together dug a trench around Madinah. Madinah was covered from three sides: on one side there were dense date palm trees and on two sides there were mountains. So only one side of the city was exposed to entry, while three sides of the city had natural obstructions. On the exposed side, the Muslims dug a trench so that the army of the opponents could not reach Madinah. When the leader of Quraysh saw the trench, he exclaimed:

By God, this is a strategy which the Arabs know not of! (Sirah ibn Kathir, vol. 3, p. 202)

The digging of the trench was a matter of strategy. A few skirmishes did take place at the time of the Battle of Khandaq when some people from the other side tried to get over the trench, but these were only one-to-one engagements.