IND was NW's largest non-hub operation....they decided to help ATA with their bankruptcy strategies...within days of ATA announcing a new hub in IND NW decided to make it a LARGE focus city....weeks later ATA decided to make MDW their hub instead....while NW did cut some flights right after ATA's annoucement they have continued to add flights up until the merger....not sure how IND stacks up against the DL focus cities though...but the legacy NW focus cities were MKE (was the largest until IND was ramped up) and GRR...SEA has always been a large international focus gateway