COVID to present we are suffering the effects of a sovereign debt bubble. Countries have more debt than they can service, therefore need to print more money to pay the interest.

2008 we had a "subprime mortgage" crisis, which meant that individual homeowners (and often multi-homeowners) were approved for debt they could have never paid back at predictable interest rates.

The reason 2008 was so remarkable is that mortgages are typically the base collateral for the financial system as they're secured against real physical homes. Banks would package all of these mortgages up and use them as a big chunk of collateral to take debt against (because who doesn't pay their mortgage!?). When retail default rates hit got high enough, the collateral that underpins so much liquidity and debt between banks became full of unpaid mortgages, slicing their value and causing the banks to margin call each other, but no one had the collateral or the dollars to post more margin. If the central bank didn't step in, then almost all "value" stored in the banking system by everyone would have effectively evaporated.

Source: My memory, please fact-check the specifics