Terra UST was the 3rd biggest stable coin and lost its $1 peg causing LUNA to spiral
Once UST lost its peg from $1 to for example $0.50, someone could buy 100 UST for $50
and redeem it for $100 of LUNA and then sell that to USDT — making money on the arbitrage.

This essentially is what triggered the Death Spiral for LUNA because the price of LUNA is
dropping with the peg, it became race to redeem for LUNA before the value drops below
the redemption price

The UST peg failed for two main reasons:
Curve pool imbalance (On Chain Selling)
$350m UST was swapped for USDT using the Curve protocol. This left a disproportionate amount
of UST versus other stablecoins in the pool for users to swap against, thus lowering the
value of UST “on-chain”
Curve is a crucial piece of the DeFi ecosystem, allowing users and dApps to swap stablecoins efficiently.
The massive selling of UST on Curve created an imbalance in reserves, leading to the value of UST falling below the peg on the protocol.

The remaining portion of UST withdrawn from Anchor protocol was sold on centralized exchanges
like Binance driving down the value on those markets as well (Off Chain)