The Taliban has retaken Afghanistan with lightning speed, forcing Americans to grapple with our 20-year-long tragedy in the war-torn Central Asian nation.

U.S. policymakers, military leaders and ordinary citizens have reckoned with such a defeat before, when the United States failed to achieve its political objectives in Vietnam. Indeed, decades later, the loss remains difficult to resolve. It’s easy to overstate the parallels between these two wars, but as the Taliban reemerges as the governing power in Afghanistan, Vietnam teaches that we’re in for an intensive battle over the past, present and future of U.S. foreign policy and military strategy.

The causes of the Vietnam debacle in the 1960s and 1970s were myriad. Top among them: policymakers’ inflated concerns throughout the war about maintaining U.S. credibility. President Lyndon B. Johnson believed the nation’s global standing against communism was at stake when he chose to go to war in Southeast Asia. After the conflict’s end, former national security adviser Henry Kissinger likewise recalled that “nothing less than America’s credibility was at stake” in Vietnam. In reality, the war hardly altered the United States’ global influence, suggesting these fears had been exaggerated.

The realization of a failed war fueled a blame game that began even before combat ended. David Halberstam’s 1972 classic, “The Best and the Brightest,” for example, concluded that “the inability of the Americans to impose their will on Vietnam had been answered in 1968, yet the leadership of this country had not been able to adjust our goals to that failure.”

Naturally, tensions erupted between the legislative and executive branches over who was at fault. President Richard M. Nixon eviscerated politicians on Capitol Hill for supposedly throwing away what had been achieved in Vietnam in a “spasm of congressional irresponsibility.” Congress responded with the 1973 War Powers Act, providing legislators the ability to review and even reverse executive decisions to send troops overseas. In many ways, Vietnam challenged Americans’ confidence in the presidency.

Saigon’s fall also placed pressures on the relationship between U.S. civil and military leaders. Senior commanders lambasted Washington elite in their memoirs, despite fairly clear evidence that victory had been nowhere in sight. Admiral U.S.G. Sharp spoke for many of his peers when criticizing “civilian politico decision-makers” who had “no business ignoring or overriding the counsel of experienced military professionals.”