The price war was swift and brutal, lasting less than eight weeks.
On October 1st Charles Schwab said it would no longer charge retail customers for trading shares,
exchange-traded funds or options online, forgoing $4.95 a trade.
The share price of America's biggest discount broker dropped by nearly a tenth.
That of its big rival, TD Ameritrade, suffered more, plunging by a quarter. TD Ameritrade followed in eliminating commissions two days later.
It had little choice, though it reckoned the move would cut its revenue by $220m-240m a quarter, or 15-16%.
On November 25th came a truce, and surrender: Schwab agreed to buy TD Ameritrade for $26bn in shares.
The deal combines Schwab's 12.1m brokerage accounts with TD Ameritrade's 12m.
It will unite two platforms used by independent financial advisers—7,500 on Schwab's, 7,000 on TD Ameritrade's—
for trading, market information and regulatory updates.
Investors in both companies will be relieved. On November 21st, when it was first reported that a deal was imminent,
TD Ameritrade's shares jumped by almost 17% and Schwab's by 7.3%.
Yet the takeover is as much a sign of the strains on big brokers as a demonstration of their market clout.
Founded in 1971, Schwab became a thorn in the sides of established stockbrokers after America's regulators abolished fixed commissions in 1975.
Ameritrade was founded the same year. In the 1990s, by then joined by E Trade, a smaller rival, the upstarts ventured online.
Ameritrade joined forces with TD Waterhouse, the discount-broking arm of Canada's Toronto-Dominion Bank, in 2006.
But in recent years digital technology has enabled an even cheaper, wholly digital, discount-broking model.
The most prominent exponent is Robinhood, a six-year-old Silicon Valley startup, which boasts 6m clients and charges nothing for trades.
It makes money from payments from marketmakers to whom it sends trades for execution,
interest from cash in clients' accounts, charging for premium services and lending stocks on margin. It has also applied for a banking licence.