American capital markets — stock exchanges, bond markets, over-the-counter markets for securities and derivatives of all types — are often praised as paragons of free-market dynamism. But beneath that reputation lies a market structure shaped less by entrepreneurial forces than by layers of regulatory design.

At the heart of Reg NMS lies Rule 611, the Order Protection Rule, which prohibits trade-throughs — i.e., executing orders at worse prices than those displayed elsewhere. This rule, intended to guarantee the “best price,” also had countless unintended consequences: it spawned an explosion of trading venues, fragmented liquidity, and a hyper-focus on speed and order type engineering.

This turf war among exchanges wasn’t a natural market realignment — it was driven by the regulatory architecture. If the best quote must be accessed and honored by law, why maintain multiple venues displaying it? The answer became clear: only those who could afford the technological and legal arms race would survive.

as of 2023, trades in US equities were routed through at least 16 exchanges and over 30 dark pools, with orders often pinging across venues in microseconds to comply with regulatory obligations rather than optimize execution quality.