HFT has rewritten the rules. It no longer takes a few weeks to crash and months to recover, America had a 1 day FLASH CRASH in May 2010, the NYSE halted, and was back the next day, all smiles, totally confused, in the dark over what had caused the event...
We now know it keeps causing these events, while removing market capital and stifling productive work.
https://en.wikipedia.org/wiki/High-frequency_trading
...At the turn of the 21st century, HFT trades had an execution time of several seconds, whereas by 2010 this had decreased to milli- (1/1,000) and even microseconds (1/1,000,000)
...On September 2, 2013, Italy became the world's first country to introduce a tax specifically targeted at HFT, charging a levy of 0.02% on equity transactions lasting less than 0.5 seconds.