WASHINGTON 

A group of former Defense secretaries and retired generals warned on Tuesday of an "exceptionally challenging" environment facing the Pentagon amid strains between the military and the civilian parts of American society.

The open letter, signed by eight former defense chiefs and five retired generals, cites "an extremely adverse environment" confronting members of the American military, which they tied to "the divisiveness of affective polarization that culminated in the first election in over a century when the peaceful transfer of political power was disrupted and in doubt."

"Looking ahead, all of these factors could well get worse before they get better," the former defense officials wrote in a letter published by the War on the Rocks website, which also reflected on the challenges posed by the COVID-19 pandemic, and the lackluster conclusions of the wars in Iraq and Afghanistan.

Those wars, they said, "ended without all the goals satisfactorily accomplished," which the US military must come to terms with as it simultaneously prepares for "daunting competition with near-peer rivals."

The signatories include both of the Senate-confirmed defense secretaries who served under former President Donald Trump -- Mark Esper and James Mattis -- as well as every retired Joint Chiefs Chairman who served since 2001: Gen. Martin Dempsey, Gen. Joseph Dunford, Adm. Michael Mullen, Gen. Richard Myers and Gen. Peter Pace.

The authors did not pinpoint blame for the ongoing situation on any political party or individual, but did note the historic nature of efforts to thwart the peaceful transfer following the November 2020 election.

They emphasized "significant limits on the public role of military personnel in partisan politics" after Trump repeatedly tried to use the military to quell popular protests against police violence in the summer of that year. They did not mention the former president's efforts directly, but said "members of the military accept limits on the public expression of their private views."

Those limits, they said, "would be unconstitutional if imposed on other citizens."

"Military and civilian leaders must be diligent about keeping the military separate from partisan political activity," they wrote.​​​​​​​