▁Pow ers ▁and ▁the ▁Ent ente ▁in ▁May ▁ 1 9 1 7 . ▁It ▁was ▁part ▁of ▁the ▁Al lied ▁Spring ▁Off ensive ▁of ▁the ▁same ▁year ▁that ▁was ▁designed ▁to ▁break ▁the ▁st alem ate ▁on ▁the ▁Mac ed onian ▁Front . ▁Despite ▁the ▁considerable ▁numerical ▁and ▁mat éri el ▁advantage ▁of ▁the ▁attack ers ▁over ▁the ▁def enders , ▁the ▁Bulgar ian ▁and ▁German ▁defense ▁of ▁the ▁positions ▁in ▁the ▁loop ▁of ▁the ▁river ▁Cr na ▁remained ▁a ▁very ▁form id able ▁obst acle , ▁which ▁the ▁Al lies ▁were ▁unable ▁to ▁defeat ▁not ▁only ▁in ▁ 1 9 1 7 ▁but ▁until ▁the ▁end ▁of ▁the ▁war ▁itself . ▁ ▁Background ▁ ▁With ▁the ▁on set ▁of ▁the ▁winter ▁of ▁ 1 9 1 6 ▁all ▁military ▁operations ▁on ▁the ▁Mac ed onian ▁Front ▁came ▁to ▁an ▁ab rupt ▁end . ▁The ▁three - month - long ▁Mon ast ir ▁Off ensive ▁provided ▁the ▁Al lies ▁with ▁only ▁limited ▁tact ical ▁success es ▁but ▁it ▁failed ▁to ▁knock out ▁Bulg aria ▁out ▁of ▁the ▁war ▁by ▁a ▁combined ▁attack ▁of ▁General ▁Sar ra il ' s ▁forces ▁and ▁the ▁Roman ian ▁Army . ▁On ▁strateg ic ▁level ▁the ▁overall ▁result ▁of ▁the ▁off ensive ▁was ▁that ▁it ▁managed ▁to ▁keep ▁over ▁half ▁of ▁the ▁Bulgar ian ▁Army ▁and ▁few ▁German ▁units ▁on ▁the ▁Mac ed onian ▁Front . ▁On ▁tact ical ▁level ▁the ▁front ▁line ▁was ▁moved ▁in ▁favor ▁of ▁the ▁Al lies ▁by ▁only ▁about ▁ 5 0