▁ 2 0 1 2 , ▁the ▁air port ▁now ▁has ▁ 1 9 2 ▁gates ▁which ▁is ▁the ▁most ▁at ▁any ▁air port . ▁ ▁In ▁December ▁ 2 0 1 5 , ▁the ▁air port ▁became ▁the ▁first ▁air port ▁in ▁the ▁world ▁to ▁serve ▁ 1 0 0 ▁million ▁passengers ▁in ▁a ▁year . ▁ ▁Historical ▁air line ▁service ▁ ▁D elta ▁and ▁Eastern ▁domin ated ▁the ▁air port ▁during ▁the ▁ 1 9 7 0 s . ▁United , ▁Southern , ▁P ied mont , ▁North west ▁and ▁T WA ▁were ▁also ▁present . ▁In ▁ 1 9 7 8 , ▁after ▁air line ▁der eg ulation , ▁United , ▁and ▁T WA ▁no ▁longer ▁served ▁Atlanta , ▁while ▁Southern ▁successor ▁Republic ▁was ▁the ▁air port ' s ▁third - larg est ▁car rier . ▁ ▁Eastern ▁was ▁a ▁larger ▁air line ▁than ▁D elta ▁until ▁der eg ulation ▁in ▁ 1 9 7 8 , ▁but ▁D elta ▁was ▁early ▁to ▁adopt ▁the ▁hub - and - sp oke ▁route ▁system , ▁with ▁Atlanta ▁as ▁a ▁hub ▁between ▁the ▁Mid west ▁and ▁Florida , ▁giving ▁it ▁an ▁advantage ▁in ▁the ▁Atlanta ▁market . ▁Eastern ▁ceased ▁operations ▁in ▁ 1 9 9 1 ▁because ▁of ▁labor ▁issues ; ▁American ▁Airlines ▁considered ▁establish ing ▁an ▁Atlanta ▁hub ▁around ▁that ▁time , ▁but ▁decided ▁D elta ▁was ▁too ▁strong ▁there ▁and ▁instead ▁replaced ▁Eastern ' s ▁other ▁hub ▁in ▁Miami , ▁leaving ▁D elta ▁with ▁a ▁mon opol y ▁hub ▁at