In May 2022, TerraUSD (UST) experienced a dramatic depeg from its $1 parity, plunging to a low of $0.68. The primary causes were a combination of factors:
Increased selling pressure on UST, as holders rushed to cash out their UST for other stablecoins, creating a "bank run" scenario.
Downward price pressure on LUNA, the collateral asset for UST, due to short-selling. This forced Terra to mint more LUNA to try and restore the UST peg, further diluting the LUNA supply.
Attempts by the Luna Foundation Guard (LFG) to defend the peg, including a $1.5 billion sale of BTC from their reserves, were ultimately unsuccessful in restoring faith in the UST stablecoin.