I normally refrain from criticizing other translations, but I draw the line on this one. The use of "massacre" here is totally wrong. يثخن simply means "to thicken," nothing to do with no massacre! In Arabic, the verb is used to indicate doing something extensively or on a big scale. Here, the subject is fighting the hostile disbelievers and the verse teaches that a prophet is not to take prisoners of war for bargaining purposes until after he has done all he can to defeat the enemy. Only Yusuf Ali got that point.
In his book بالحجة والبرهان لا نسخ في القرآن, page 168, Husaam Rushdi Al-Ghaali propounds the varied interpretations of the scholars of the word يثخن
. He said Ibn Abbaas, may God have been pleased with him, said it means To prevail. Al-Bukhaari, rahimahullah, said it means to conquer. Al-Ghaali opines like I did in the quote above: that first comes victory then prisoners of war are taken.