A wave of mergers in many sectors of the economy over the last several decades has significantly reduced competition and hurt consumers. That’s why the lawsuits filed last week by the Department of Justice and state attorneys general in federal court challenging two big health insurance mergers were so important.

Antitrust officials say Aetna’s $37 billion acquisition of Humana and Anthem’s $54 billion purchase of Cigna will reduce the number of large national health insurers to three, from five today. That would lead to fewer choices and higher premiums for individuals and employers in places like New York, Los Angeles and Kansas City, Mo. The mergers could also hurt doctors and hospitals, because they would have less bargaining power against the larger insurers when negotiating reimbursement rates.

These two proposed mergers are the culmination of a series of deals in the health care industry that have reduced the number of insurers and caused the consolidation of hospitals and doctors’ practices everywhere. Every merger seems to compel another as competitors bulk up, lest they find themselves with less leverage in negotiations between insurers and providers.

Health industry executives, including those at Aetna, Humana, Anthem and Cigna, have typically defended these mergers by arguing that they are necessary to make the health care system more efficient. They also say they allow doctors and hospitals to better coordinate medical care by, for example, having different specialists working for the same hospital or covered under the same insurance policy — something they argue is encouraged by the Affordable Care Act, the 2010 health reform law. (Aetna and Humana and Anthem have said they will fight the antitrust suits, which were filed in the United States District Court for the District of Columbia; Cigna says it is evaluating its options.)