It's interesting to think about how world leaders take lessons from global crises and then apply them to ensuing situations where they may no longer fit. It's even more interesting to wonder which current events will eventually be understood as this phenomenon.
After World War 1, Europe learned that technology had (finally!) made war too costly and bloody, and that it should (finally!) be avoided at all costs. Fast forward into the 1930s and, with this lesson top of mind, you can understand why Chamberlain was so desperate to appease Hitler and avoid a repeat of World War 1.
Of course, World War 1, Act 2, did happen, and world leaders took from it a new lesson: Defeat dictators before they lay eggs.
The Cold War and its proxy conflicts came next, and American leaders had one thing on their minds: Avoid the mistakes of World War 2 by snuffing out evil powers in the crib. Hitler was allowed into Czechoslovakia, Austria, and the Rhineland before a line was drawn at Poland when it was nearly too late -- so this time, things would be different! So what did that mean? Containment and proxy wars with the Soviet Union over places like Korea and Vietnam, which for fucks sake just wanted its freedom after a century of European occupation.
After the Vietnam War, the elevation of oil on the world stage shifted international focus to the Middle East. (Before the 1980s, almost no American servicemen had died in the Middle East. Since the 1980s, almost no American servicemen have died anywhere else.) This transition may have reset things a little bit, but in time new lessons emerged and began to shape subsequent decisions. All of us are currently the summation of the above lessons, and hundreds more; but the challenge is to understand current situations well enough to know which lessons fit into the puzzle at hand. The difficulty in doing this right is, of course, why leadership is hard.
Some "truths" I see currently (or recently) defining American foreign policy:
1 - Invading Iraq to topple Saddam Hussein was a mistake, especially given the lack of an exit strategy. Don't do it again!
Current application: Leave Syria alone! Assad may be one of the most callous and brutal dictators of our time, but he's better than a long war and power vacuum.
Confidence rating: Iffy. Who the fuck knows? Assad is destabilizing THE ENTIRE WORLD, so are we sure it's best to leave him in his little corner to torture and mutilate his innocent citizens? Are we sure an international commitment to human rights would backfire so dramatically?
2 - The Cold War was four decades of pointless hostility and proxy wars. Don't do it again!
Application: Putin might suck, but he's not as bad as another Cold War. Just like Chamberlain appeased Hitler in the 1930s, the West has repeatedly appeased Putin, turning a blind eye to his phony elections, domestic political terrorism, and (until recently) obvious meddling with Western democracies.
Confidence rating: Low. Putin lives to personally profit from Russian natural wealth, not conquer the world, so he's probably a low risk to become the next Hitler. However, he's an extremely HIGH risk to continue driving wedges between his democratic neighbors so that Russia's status quo as a petrol-state may continue at least through his lifetime. After that, Putin certainly couldn't care less.
And World War 3 with Putin is not the only other option since he's a gangster, not a warlord. Something like 1/3 of Europe's oil imports come from Russia, contrasted with Russian exports, roughly 3/4 of which go to European markets. This gives all the power to the EU, should it gather the courage to feel a short-term pinch in the name of human rights, democracy, and free speech; and ultimately stand up to Putin through trade and diplomacy.
3 - Waging war in the Middle East is part of what focuses Islamic militants on the West in the first place. Don't do it again!
Recent application that I advocated for: Don't declare war on the Islamic State. ISIS is abjectly insane, but we helped create them from so many past conflicts. Sure, we might defeat ISIS, but what new acronym will replace it?
Confidence rating: Super low, since I was pretty obviously wrong. ISIS was almost certainly worth of sustained military action, and we may have even done this one correctly by assisting local forces and avoiding US boots on the ground, yet still defeating the cult. Had Obama and then Trump listened to me, much would be worse off.
Predicting outcomes is hard.
These are obviously only three such observations about how hard-learned lessons can occasionally overstay their welcome. There are certainly other lessons being precariously applied right now, along with yet more lessons being learned right now. I can't help but wonder what lessons the United States will take from its 2016 mistake and how those ideas will shape possibly unrelated policy in the 2020s and beyond.