In all the battles fought during the time of the Prophet (saww), the combined fatalities on both sides did not number more than 1,000 in total. The message of Islam was not spread by sword. I am all for Sharia and living in the peaceful, harmonous and spiritual environment that Islam promises. But I am against the killings of innocents to reach to this dream.
well the scale of battles in prophet's time and later is also a big indicatior of why that happened.
except for taif all battles were small term affairs , taif and khyber is the biggest siege operation and attrition campaign.When muslims encountered huge armies casulties were large ( Mootah). But most tribes were won over by diplomacy so there was little need for prolonged warfare.Here arab and tribal solidarity played cruical roles.
These were less factors when muslims faced bigger imperial armies and thus bloodshed was much greater.Even then it was nothing on the scale as compared to roman-carthagian or roman-sasssanian wars.
killing of innocents is less likely to occur in small engagements but in open warfare and gbig engagements it is sometimes inevitable.