Assalamo alaykum, its real prey when any muslim meets to any as it means to make request to Almighty Allah swt to bestow on u pease & blessings ever. its also made compulsory to reply this doa as just to reply as v also prey for u same things wa alaykum salam Alhamdo lillah history of mankind shows us there may be war but always love wins ever. what any body justify innocent killing by any terrorist.no never its crualty no religion allows innocent killings & islam does not allow even to kill wemans old folk ,kids, tree,any greenary ,or hospitals prey places. they why any one shud name it islam its all harrashment to mankind no religion need to be spread its a feeling automatically spreads in humans when u deal with peace & real follow the Al quran & sunnah ,it never b under cover it smelt in any forms u spread love /pease has its frangrence pl do it find in secrifice to serve mankind by spreading real teachings of islam, hope u may find the real path Allah swt wants u to walk sirat