The South Korea stock market crash of 2026 erased a quarter of the country’s benchmark index in 21 days and force-liquidated 320,000 retail accounts — many of them overnight. The reason it matters far outside Korea: the crash was a smaller, faster version of the exact leverage machine now running under the US market, where margin debt just hit its highest level ever recorded.

That is the argument YouTube finance creator Andrei Jikh laid out in a July 20, 2026 video, and the parallels are hard to unsee.

Key takeaways

  • South Korea’s KOSPI fell about 25% in 21 days, triggering margin calls on 1.2 million accounts — roughly one in every 30 people in the country — and liquidating over 3 trillion won in stock.
  • The market was dangerously concentrated: just two AI-memory chipmakers, Samsung and SK Hynix, made up over 56% of the entire KOSPI, bought heavily by ~14 million leveraged retail investors.
  • The trigger came from the US — a late-June sell-off in American chip stocks ahead of Micron earnings spread to Korea’s two-stock market and detonated.
  • US margin debt hit ~4.5% of GDP in June 2026, the highest reading in American history — above the dot-com peak, 2007 and the 2021 meme-stock bubble.
  • One number holds up the whole trade: the AI capital expenditure of Microsoft, Google, Amazon and Meta. A single hyperscaler capex cut is the domino to watch.

What happened in the South Korea stock market crash of 2026

Three weeks before the crash, South Korea had the best-performing major stock market on Earth. The KOSPI index had climbed almost 200% in twelve months, against roughly 24% for the US S&P 500 over the same stretch, according to figures cited by Andrei Jikh. At one point Samsung was up over 500% and memory-chip maker SK Hynix was up more than 1,000% — a 10x.

That rally was built on an extreme concentration. In the S&P 500, the top 10 companies are about 36% of the index — already historically high. In the KOSPI, two companies alone, Samsung and SK Hynix, made up over 56% of the whole market. In practice, Korea’s “diversified” index traded like a single volatile chip stock.

Then it snapped. Over 21 days the KOSPI dropped about 25%. On the day Koreans now call “Black Tuesday,” the index fell more than 10% in a single session — one of the worst days in its history. For scale, a 10% one-day drop in the US would rank as the third-worst day in American market history, behind only 1987 and the Great Depression.

How leverage turned a sell-off into a doom loop

Korea’s crash was violent because of how the market was owned. Around 14 million people — one in four Koreans — are retail investors who call themselves “ants”: individually small, collectively market-moving. Priced out of housing, a generation treated the stock market as their last realistic path to wealth, and many went in with borrowed money.

A lot of that money went into leveraged ETFs — funds that multiply daily moves, so a 3x fund turns a 10% drop in SK Hynix into a 30% loss. At the peak, Koreans had poured roughly 10 trillion won into leveraged funds betting on a single company, per figures in the Jikh video.

Leverage is what removes the human “stop” from a sell-off:

  • When leveraged positions fall to a set price, brokers issue a margin call — deposit cash by morning or your shares are sold at any price.
  • That forced selling pushes prices lower, triggering the next group’s margin calls. A self-feeding doom loop.
  • Leveraged ETFs must rebalance daily, so they sell into a falling market to hold their ratio — dumping on top of the liquidations.

Normally about 2% of Korean margin accounts get force-liquidated; during the crash that ran above 10%, roughly five times normal. In total, 1.2 million accounts hit margin-call thresholds and more than 3 trillion won was auto-sold. The contagion spilled across Asia — over $600 billion was erased from regional markets, with Japan down more than 4% — and at one point the only thing that stopped the KOSPI’s slide was a national holiday closing the exchange. South Korea’s president, who had spent a year encouraging citizens into stocks, called an emergency stabilization meeting.

What actually popped the bubble

The spark did not come from Korea. In late June 2026, US chip stocks began selling off as investors turned nervous ahead of earnings from Micron, America’s largest memory-chip maker and a direct competitor to Samsung and SK Hynix. When US memory names fell, Korea’s two-stock market fell harder — first ~4.6% in a session, then Samsung and SK Hynix down more than 9% in a day, then Black Tuesday.

The deeper link is money. US hyperscalers — Microsoft, Google, Amazon and Meta — spent roughly $376 billion on AI infrastructure in 2025 and are on track for about $725 billion in 2026, and a large slice flows to Korean memory suppliers. Korea’s retail investors were, in effect, making a leveraged bet on American AI spending continuing forever. This is the same demand engine we mapped in the AI supercycle running through compute and energy.

Why record US margin debt is the real warning

Here is the uncomfortable mirror. US margin debt — money Americans borrow to buy stocks — reached about 4.5% of GDP in June 2026, the highest level ever recorded, according to the reading released that week. Every prior spike to an extreme (1968, 1972, 1987 before Black Monday, March 2000 at the dot-com peak, July 2007, 2018, 2021) preceded a crash. The current figure sits above all of them.

Worse, it is an undercount. Official margin data tracks only traditional brokerage loans — it misses leveraged ETFs, zero-day options, portfolio margin and private credit. The same category of leveraged single-stock ETFs that blew up Korean investors trades here too, including 2x funds on Nvidia and Tesla. FINRA publishes the official US margin-debt statistics for anyone who wants the floor number.

Concentration rhymes as well: the S&P 500’s top 10 names are ~36% of the index and nearly all are making the same AI bet. Nvidia sells the chips, Microsoft, Meta and Google buy them, Micron supplies the memory, and revenue circulates between them — one company’s spending is another’s earnings. That circularity is part of why Bitcoin can fall while these stocks keep rising: capital has crowded into a single trade.

The one number holding up the market

Short-seller Jim Chanos — who famously called Enron — argues the returns on AI spending are already fading: hyperscalers earned about 40 cents of operating income per incremental dollar invested 18 months ago, roughly 20 cents today, and are heading toward 10. His timing call for the reckoning is “late 2026 or 2027,” when a trillion-dollar CEO finally asks whether the next $1 trillion of capex earns more than Treasuries would.

So the single number to watch is the combined AI capital expenditure of Microsoft, Google, Amazon and Meta. Korea crashed on the fear that memory demand might slow — not that it did. The precedent is Cisco in 2000: when customers like Coca-Cola cut router orders, Cisco’s earnings collapsed and the Nasdaq fell 78%. A 20% hyperscaler capex cut wouldn’t dent the hyperscaler much, but it would gut the earnings of Nvidia, Micron, Samsung and SK Hynix. The unwind begins the day the market rewards the first company to cut AI spending instead of punishing it. For the fuller checklist of what to watch, see our breakdown of when the AI bubble might pop.

Two scenarios remain live. In the first, Korea stays contained, memory prices hold, hyperscalers keep spending through 2027 and the KOSPI recovers. In the second, Korea was the first domino — and a 4.5%-of-GDP margin-debt market gets to find out what a forced-selling doom loop looks like at US scale.

Frequently asked questions

What caused the South Korea stock market crash in 2026?

A late-June 2026 sell-off in US chip stocks ahead of Micron’s earnings spread to Korea’s KOSPI, which was over 56% concentrated in two AI-memory makers (Samsung and SK Hynix) and heavily owned on borrowed money. As prices fell, margin calls forced automatic selling, which drove prices lower and triggered more margin calls — a doom loop that cut the index ~25% in 21 days.

How many accounts were wiped out in the KOSPI crash?

Around 1.2 million accounts — roughly one in every 30 people in South Korea — hit margin-call thresholds, and 320,000 accounts were wiped out, some overnight. More than 3 trillion won in stock was auto-liquidated by brokers, according to figures cited in Andrei Jikh’s July 2026 video.

Is the US stock market at risk of the same crash?

Structurally, the ingredients are present. US margin debt reached about 4.5% of GDP in June 2026 — the highest ever recorded — the S&P 500’s top 10 stocks are ~36% of the index and mostly bet on AI, and the same leveraged ETFs that hurt Korean investors trade in the US. The catalyst to watch is a cut in AI capital expenditure by Microsoft, Google, Amazon or Meta.

What is a margin call and why does it force selling?

A margin call happens when stocks bought with borrowed money fall to a set level and the broker demands more cash by the next morning — or sells your shares at whatever price the market offers. Because the sale is automatic, it doesn’t wait for a recovery, and the extra selling can push prices down enough to trigger the next investor’s margin call.

This article is analysis and reporting, not investment advice. It is based on the source video below and public data; always do your own research.