Hospital systems were merging before the Affordable Care Act passed, but the law has thrown fuel on the fire. And by "fuel," I mean money. Hospitals justified their mergers by claiming they helped reach economies of scale. But the mergers also reduced competition, helping the hospital systems negotiate higher reimbursements from health insurers. Then came the A.C.A., which envisioned large, integrated provider networks, and the government was willing to hand out billions of dollars to providers that successfully implemented the government's vision of quality care.