In 300 BC, when King Min took the throne, Qi was among the strongest states in China's Warring States period, if not the most powerful. But his corruption and incompetence were so legendary that in 284 BC, it was completely conquered by Yan, and King Min was executed. Oh wait, Qi was ALMOST completely conquered; although seventy cities were taken, two remained independent — which was enough for Wangsun Jia and Tian Di to reconquer all the land Yan took.
By 208, Cao Cao's forces controlled two thirds of China's people and was on the brink of unifying it. Then came the Battle of Chibi; against all odds, Cao Cao's forces were nearly annihilated, and China would remain divided for another seventy-two years—and that only briefly, remaining unified for about 25 years before falling into disunion again for nearly 300 years after that.
The Roman Republic during the Punic Wars, especially after Cannae. It's estimated that the battle wiped out a whopping 80% of the entire Roman army. This catastrophic loss drove people to such despair that the Romans actually performed acts of Human Sacrifice to appease the Gods who seemed to have abandoned them. They then spent the next few years steadily supporting and helping their clients in a war of attrition, enjoying a lucky break with Hannibal Barca not marching straight to Romenote or so it seemed to them at the time; Hannibal had no practical way of breaching the city walls, couldn't starve the city because of the Tiber river, had poor experience with sieging as demonstrated with Saguntum, and didn't have the numbers or supplies to maintain a siege while the other Italian cities remained loyal to Rome. Thanks to generals like Scipio Africanus and Marcellus in addition to the Romans' massive pool of manpower, eventually the Romans built a new army from scratch, out-strategized the Carthaginians, turned their Numidian cavalry against them, and came out on top at the Battle of Zama.
The Crisis of the Third Century had two moments where The Roman Empire was on the brink. Picture yourself as Gallienus in 260 alongside your father Valerian. You just heard that your father got captured by Sassanids. On this news a revolt in Pannonia broke out. When you went to quell this revolt, your general Postumus killed the emperor’s son and proclaimed his own realm in Gaul, Spain and Britannia. After killing that one usurper in Pannonia, you went to deal with another but got delayed, because the Allemani invaded Italy. You crushed the Allemani, but in the meantime another usurper revolted in the Balkans, then another one in the east, then one in Egypt (the breadbasket of the empire, mind you). While it’s all happening, the Eastern provinces are being overrun by the Sassanids, the goths take to the sea and are ransacking Greece. And I also forgot to mention that the during all this time, the pandemic of Cyprian plague has been ravaging the empire, reducing it’s manpower and tax base. These circumstances seem almost too terrible to be true, but that was what Gallienus had to do. He managed to suppressed every usurper that wasn't Postumus and every barbarian invasion was repelled. Now imagine yourself as a Roman citizen in the 270. The senate has just proclaimed Quintilius as emperor whilst the army proclaimed the usurper Aurelian as emperor. Tetricus still holds the provinces of Gaul and Britannia, whilst Zenobia took the Roman East as her new Palmyrene Empire. The empire is divided in 4, disease was rampant for both the army and the citizens, the roman currency is almost worthless from inflation, the threat of famine is possible without Egypt and the Juthungi tribe were on their way to sack Rome. For the empire to recover all of this within a few decades is nothing short of a miracle.
The Byzantine Empire that followed up The Roman Empire had a habit of this. While territory was lost multiple times, crafty emperors found ways to come back from massive defeats and humiliations time and time again. While they eventually were conquered by the Ottoman Turks, by that point they had come back enough times from near destruction that historians ponder if they could have recovered just as they had against the Arabs and the Seljuk Turks with a comparatively minor change of events.
By the time Alfred the Great came to power as the king of Wessex, the fledgling kingdom was the only Saxon kingdom left in England, with every other one fallen to the invading Danes. Unfortunately for the Danes, turns out Alfred the Great was a colossal Badass Bookworm to the Nth degree. Between organising a rebel army in the swamps and dressing as a bard to infiltrate Viking camps and learn their plans, he defeated the Danes decisively at the Battle of Edington, then used the resulting peace to build up a network of defences to make his kingdom impregnable, while also doing other awesome things like codifying a system of laws and building the framework for an education system. Alfred was also savvy enough to realize that the Vikings didn't have much knowledge of siege warfare, and that most of them returned home to Scandinavia when the raiding season was over. So instead of throwing away men on grand pushes to take back the entire island, he focused on securing and fortifying each town they recaptured, slowly retaking the island one mile at a time. When he died, his son and daughter went on to deliver crushing defeat after crushing defeat to the Vikings and reclaim all the territory lost over the years. His grandson Athelstan mopped up the last Viking enclaves and became the first king of a unified and powerful England which was never threatened by invading Scandinavians ever again (bar the invasion by Cnut, and Harold, and...).
The reinstatement of Admiral Yi Sun Shin. After several dramatic victories against the Japanese invasions (1592-1598), he was rewarded in 1597 with accusations of treason, arrest, torture, and demotion to foot soldier. His successor proceeded to lose the entire Korean navy in a single battle through startling incompetence, leaving only 13 ships that had withdrawn rather than fight (none of which were the famous turtle ships). After being restored to command and rallying what was left of his fleet, Admiral Yi proceeded to fight a fleet of 133 Japanese warships and over 200 support craft, routing his foe while destroying 31 enemy ships outright and crippling over 90 more, with no losses. Japanese morale was, fairly understandably, crippled by this, and the Koreans would win every naval engagement until the end of the war.
Happens multiple times during the Thirty Years' War. First Bohemia revolts and throws Imperial forces out of Bohemia. The Empire strikes back, including beating an attempted Danish invasion, and looks on the verge of total victory. Cue Swedish intervention, that in a few years completely shatters the imperial stranglehold on northern Germany and has Swedish troops as far south as Munich. Then Gustav II Adolf dies, the Protestant alliance falls apart and the Emperor manages to drive the Swedes back to the Baltic again. And we're only in the 1630s! France enters the war and it is finally brought to a negotiated settlement, with France and Sweden the nominal victors.
By 1709, the War of the Spanish Succession was going very badly for France. The French had suffered multiple defeats at the hands of their Allied opponents, the costs of the war were staggering, and France was ravaged by famine. French King Louis XIV was at the end of his rope and tried to open peace talks, offering to give up almost all his military conquests during his reign. The Allies foolishly rejected this and demanded that Louis's grandson Phillip V give up the Spanish throne and that Louis forcibly remove Phillip if he refused. An outraged Louis broke off negotiations and resumed the war, saying that if he had to fight he would rather battle his enemies than his own family. Louis wrote a letter to his people that was read in every parish in France, urging them to one last stand. From the king on down, the French scraped together the money to rebuild their armies and started turning the tables on their Allies. The French inflicted a Pyrrhic Victory on the Allies at the Battle of Malplaquet and outright won the Battle of Denain, preventing an invasion of France, while Franco-Spanish victories in Spain itself secured Phillip's throne. The British were increasingly unhappy at how much blood and treasure the war was costing them, especially when a decisive victory became increasingly unlikely. They signed a peace deal with France that gave them valuable commercial and territorial gains, while also ensuring the French and Spanish Crowns would remain separate. The rest of the Allies were unhappy at this, but they were too exhausted to continue on their own and also settled with France.
In the Seven Years' War, Prussia was badly outmanned and outgunned and its only ally (Britain) was busy fighting France and did not much care to save them. Then the Austro-Russian alliance does not march on Berlin (which was virtually undefended) and the Russian Czar dies. The next Czar is a great admirer of Prussia and its leader and the country is saved once more. A hundred years later Prussia would establish the German Kaiserreich. Another forty years after that the Prussian led Kaiserreich would go toe to toe with the rest of the world and come within an inch of winning bringing France to the brink of defeat and causing the utter collapse of Russia in the process.
The most famous Real Life example would be John Paul Jones, and is actually the original source of the quote "I have not yet begun to fight" which has then been parodied ever since. With his ship, the Bonhomme Richard burning and sinking, and the flag (aka "the colors") shot away ("striking the colors" was a symbol of surrender); one of John Paul Jones officers, apparently believing his captain to be dead, shouted a surrender. The British commander asked if they had struck their colors. Jones replied: "I may sink, but I'll be damned if I strike!" Eventually Jones won the battle and transferred his command to the captured enemy ship as his own ship sank.
France during The French Revolution was on a low ebb in 1793, its armies were suffering setbacks, the Austrians were marching to the capital and General Dumouriez, the hero-general of Valmy had become a defector along with other nobles. The coalition now included England who put a blockade on all food imports, the famine was increasing and there was political instability like no tomorrow with many people expecting that the New Republic would be easily defeated and steamrolled. So what do France do? They got their act together, discover their revolutionary spirit and start winning. In the space of a single year, the French expanded their army by mass conscription, restructured it from the ground up while pioneering administrative reforms that put them ahead of the rest of the Continent.
Carl von Clausewitz: "In 1793 such a force as no one had any conception of made its appearance. War had again suddenly become an affair of the people, and that of a people numbering thirty millions, every one of whom regarded himself as a citizen of the State... By this participation of the people in the war... a whole Nation with its natural weight came into the scale."
World War I. By early 1918, Imperial Germany had practically conquered Eastern Europe, were about to come to a permanent peace settlement that would give them most of their conquests, all the Central Powers were — while shaken — still in the fight, and the Balkans front had been effectively pacified with the fall of Romania and Serbia. The Germans and Austro-Hungarians were shifting forces for two massive simultaneous assaults to try and destroy the Western Allies by striking both in France and Italy — and would drive so far that they began minting medals in preparation for the falls of Paris and Venice, all while the Entente could not even divert needed units from Africa because of Paul von Lettow Vorbeck's guerilla actions and the Senussi rebellion. The only GOOD news for the Western Allies was that the US had now entered the war, but it was stuck with a seriously under-strength, under-equipped, undertrained, and under-experienced force on the wrong side of the Atlantic Ocean. Then came the Balkan offensive, the Turkish surrender, Armando Diaz's reforms and "three great campaigns" to annihilate the Austro-Hungarian Empire, Belleau Wood, Amiens, the Hundred Days, and finally the October mutiny that struck at the heart of the Kaiserreich.
The early days of the Korean War. Vastly enlarged and lavishly supplied and backed by Soviet equipment and advisors, the North Korean military pushed South of the DMZ and readily routed every United Nations force that tried to halt or at least delay it, to the point where all that the UN were pushed back to their final stronghold at Pusan and the surrounding towns, which the North Koreans rapidly besieged using superior numbers and equipment, with the UN commanders there living hand-to-mouth on reinforcements from Japan, and even THEN the North Koreans came close several times to crushing the main line of defense and taking Pusan. And THEN Inchon happened, which saw the North Korean military be encircled, decimated, and forced to retreat North while much of its strength was trapped in the South and destroyed. This war swung both ways, too. When the Chinese intervened, it was explicitly because the UN had reached from the DMZ all the way to the Yalu River. The very same Yalu River that serves as the Korean northern border, in fact - last stop, final destination, end of the line. The Chinese proceeded to demonstrate every guerilla and mass warfare tactic they learned in their Civil War to retake all of North Korea and reach shelling range of Seoul before their offensive was finally stopped, with the final result being...the border ending up right back where it started, give or take a few kilometers.
In mid-2015, the Syriancivil war had been grinding on for over 4 years. Under fire from ISIS, the al-Nusra Front, and dozens of other rebel groups, it looked like Bashar al-Assad and his Syrian Arab Army were on their last legs. The United States along with other powers in the region such as Turkey and Saudi Arabia were already making plans for a Syria without Assad. Then in September 2015, Russiaentered the fray on Assad's side. With backup from Russian airstrikes, armor battalions, and special forces, the SAA began to make a real comeback, and as of 2016 Assad re-emerged as a viable player in the war.
Others
There is some evidence that humanity as a whole has been through this at least once. At least if the Toba catastrophe theory is to be believed...
By the late 90's, all of the competitors to the IBM Personal Computer and Microsoft Windows had been driven out of the market except for Apple, whom many predicted would not last much longer, or perhaps even forced to abandon the Macintosh platform and make PCs instead. Their market share had shrunk considerably, with seemingly little chance of improving since their nearly decade-and-a-half old classic Mac OS was woefully out-of-date, lacking key modern operating system features like protected memory and preemptive multitasking. Having failed to develop a replacement OS in-house, Apple decided to acquire one the outside, and chose to purchase NeXT, the company that Steve Jobs had started after he left Apple due to Creative Differences over a decade prior. Though he was only an "advisor" at first following the acquisition, he quickly became interim and then fulltime CEO, and proceeded to revive the company with exciting new products such as the original iMac, Mac OS X, the iPod, and eventually the iPhone. Today, Apple, far from being on the brink of going out of business, is one of if not the most successful companies in the world.
The Fire Emblem series had fallen on hard times going into the 2010s, with the last major releases in the series, Radiant Dawn and Path of Radiance, underperforming. Believing that the series was running out of steam, Nintendo gave developer Intelligent Systems permission to work on one more game, with the condition that if this game also failed to succeed, the series would be retired. The end result was Fire Emblem: Awakening, a game that would serves as the series's Swan Song if it failed to succeed, featuring elements from past games meshed into a big love letter to the fans. It quickly went on to be a Killer App for the Nintendo 3DS, and the series has enjoyed continued success ever since.
In Politics, the 2018 midterm elections could count as this for the Democratic Party. Democratic Party was talked about as if it would fall apart soon (Given the grave losses suffered at all levels in the preceding years, Donald Trump wining the 2016 election, and the infighting, this was understandable). With the 2018 midterms, the Democrats gained seven governorship's, flipped the House of Representatives, and gained 350 state wide seats.
Joe Biden's 2020 presidential campaign certainly seemed to be on the ropes, on the verge of collapse following serious defeats in Iowa, New Hampshire, and Nevada. Then he won a crushing victory in South Carolina and won a landslide victory on Super Tuesday, effectively ensuring he would win the nomination.
, and is actually the original source of the quote "I have not yet begun to fight" which has then been parodied ever since. With his ship, the Bonhomme Richard burning and sinking, and the flag (aka "the colors") shot away ("striking the colors" was a symbol of surrender); one of John Paul Jones officers, apparently believing his captain to be dead, shouted a surrender. The British commander asked if they had struck their colors. Jones replied: "I may sink, but I'll be damned if I strike!" Eventually Jones won the battle and transferred his command to the captured enemy ship as his own ship sank.