The fall of Saigon happened before I was born so I have no direct memories of the debacle that was the Vietnam War and its ignominious end, only the images, interviews, and the excellent documentary from Ken Burns to imagine what it must have been like to have lived it firsthand. The primary purpose there was to stop Ho Chi Minh and the "Communist threat," which we spectacularly failed to do.
When we went into Afghanistan it was with a different primary purpose: find Osama Bin Laden and bring him to justice for 9/11, whatever that entailed. I was in support of that mission then and remained so until Bin Laden was eventually killed in Pakistan in 2011.
I was deeply uneasy, however, about our approach to Afghanistan as a country, mostly because of what I learned from our disastrous intervention in Vietnam. Somehow, we would have to deal with the Taliban in a substantive way and find a way to integrate them into the government or it would be an exercise in futility, imposing a puppet democracy over what is ultimately a religious oligarchy and has been for decades. Our involvement in others' civil wars has proven time and again that American ideals do not work as a one size fits all solution, but our insistence that "we must be right and we know what's best for these civilizations" makes that an untenable thought for many Americans, and we hurl money and men at the country as if by sheer numbers we can turn the ideological tide.
I won't say I told you so because I couldn't say anything to anyone who would have any actual impact on US's choice to invade, nor could I see the future, just make some educated guesses. Even then I cannot truly understand the region and its warring sects, the full history of Afghanistan, or all of the geopolitical forces that push and pull across the Middle East. I am no diplomat, and would be woefully unqualified and under-prepared to contribute anything of significance to the discussion, so just watched with a sense of dread as we started to search for democracy where there was none.
As a country, yes, we couldn't have let 9/11 go unanswered; that was a direct attack of the most brutal nature and a clear declaration of war, regardless of who had carried it out. But going to war with a national power like Germany or Japan in WWII is a far cry from trying to declare war on a religion or extremist group with no centralized base. The idea of the War on Terror was sound, but the implementation needed to focus on Al Qaeda and Bin Laden, not Afghanistan or Iraq. Once we overthrew their governments instead of operating in the gray areas of negotiating to let the CIA handle Bin Laden, we were in all likelihood doomed to see another precipitous evacuation ahead of total defeat. It would have happened if the president was Republican or Democrat. It would be the one who was willing to say "Enough. We are done."
So here we are again, watching our allies desperately run for aircraft and the Taliban taking over. In Iraq there will probably be similar scenes when we finally decide to cut our losses and watch chaos engulf that country as well. We met our primary goal, but lost any other gains we had made in and for Afghanistan itself as we expanded our aims.
The next generation will do the same for Afghanistan and Iraq as I did with Vietnam, watch the footage, read the news reports and analysis from experts in the field, and hopefully absorb and apply the lesson: when it comes to deposing governments in countries halfway around the world, don't do it. Focus on the true enemy and find a subtler way to address the threat. Choose an appropriate primary endpoint, accomplish it, then withdraw and don't take ownership of the country's future moves. It rarely ends well otherwise.