Ben Radclyffe from BitMex, focused his presentation on market makers. Prior to market makers, finding liquidity in the market was tough. Often times it was hard for the buyers and sellers to find an equilibrium. Market makers entering the market may have added a premium, however they also offered liquidity for traders. Now, adding in market maker competition, the spread is reduced and much more liquidity enters the market.
After introducing many more stocks and electronic trading, the spread reduced to pennies and the trading volume increases exponentially.
In his presentation he also talks about the latency rabbit hole which is a trading fund shortening the distance to the server of the exchange to get an edge over their competition.
I urge you to watch his presentation to get the history and current system of trading with markets makers.
