Think of Wall Street without JPMorgan Chase & Co. or try to imagine Bay Street without RBC Dominion Securities Inc. It is unthinkable that the muscle dominating America’s financial marketplace should not carry a U.S. passport. But in London, the British are once again getting used to the idea that in the City of London, the world’s premier financial marketplace, no U.K. bank will be making the big moves. Barclays PLC has signalled its retreat, sacking 7,000 investment banking staff and withdrawing from big, expensive bond and commodity trading activities. Barclays Capital, the last remaining British contender for the title of Master of the Universe, has thrown in the towel; the fight to win the biggest slice of the tiny margins in managing global money flows is now mainly a struggle between Americans, a German and a Swiss. The question is whether it matters.