Star Trek:
Picard has shades of this as the galaxy has not become a more peaceful place since the Dominion War ended. Also the failure of the treaty with the Cardassians in both The Next Generation and Deep Space Nine.
As there's a restriction on Real Life examples explained on No Recent Examples, Please!, but it isn't currently on the trope page itself, there's a proposal to add it under discussion on the Trope Description Improvement Drive thread. Please comment there if you have a view.
Vietnam is not remotely this. The US gave up, France gave up, and South Vietnam and the US and China-backed Khmer Rouge were defeated. North Vietnam is the undisputed winner outside of revanchist stab in the back fantasies of american nationalists.
This is much too complex and contentious area to box up as this trope. It just looks like shoehorning some history that vaguely matches the template.
- The American Civil War's ultimate cause is debated to this day, but one positive outcome of the war is the freeing of the slaves. Unfortunately, after a decade or so of remarkable steps forward in civil rights for the freed slaves, there was a giant leap back, with imposition of Jim Crow laws, segregation, disenfranchisement, and terrorism against blacks. The South made a huge political comeback, and with the rest of the country acquiescing, progress in civil rights stagnated. African-Americans became second class citizens for a century after being ostensibly freed in the war.
Hide / Show RepliesThe federal government was dominated by the Republican Party for a generation after the war, which paved the way for the graft and corruption that characterized the post-war years. Not that the Republicans were especially corrupt; they just had an easier time of it without a strong opposition party.