Automated trading is nothing new, and it has been going on for years, ever since computers were able to be programmed. However, their use has become more widespread today, and the trend seems to be shifting further away from human trading.
The National Market System (NMS) allowed for increased transparency in the markets in 2007. The idea was to improve price discovery and reduce chances of fraud. In a decentralized market, the retail brokers can set their own bid and ask prices, unlike what would happen through an exchange.