Interesting topic. I'm going to suggest that no, initially, like Christianity, Islam was not spread by the sword. Later, yes, Islam was spread by the sword as it was the religion of Arab colonialists. So, again, initially no, but later, in certain times and places - of course.
Which Arab colonialists came later?
See this:
Richard Bulliet's "conversion curve" shows a relatively low rate of conversion of non-Arab subjects during the Arab centric Umayyad period of 10%, in contrast with estimates for the more politically multicultural Abbasid period which saw the Muslim population grow from approx. 40% in the mid 9th century to close to 100% by the end of the 11th century.[10] This theory does not explain the continuing existence of large minorities of Christians in the Abbasid Period. Other estimates suggest that Muslims were not a majority in Egypt until the mid-10th century and in the Fertile Crescent until 1100. Syria may have had a Christian majority within its modern borders until the Mongol Invasions of the 13th century.
source: Tobin Siebers, "Religion and the Authority of the Past", University of Michigan Press, Nov 1, 1993, ISBN 0-472-08259-0
Its possible the Mongols forced people to convert since they came later although it doesn't seem very Mongol like, but they did eventually get more civilised since as Mughals they ruled India for 800 years without much impact on religion.
Historically it's probably not true at all
