After Nelson's victory at Trafalgar, GB had delivered a global message loud and clear "We took out Napolean's France and the Bourbon Spanish fleet, we can take you out too". Global security for trade at the time was provided by the Royal Navy. Financial security for the investor was given as Lloyd's of London ensured a way to hedge against losing your entire shirt, should the ship you bought 20% stake in not return. The a market ripe for the middle-class titleless but incredibly affluent landed gentry (because no one of title would ever be considered a worker, how disgraceful!) to re-invest the profits gained from industrialization into other ventures.
The other (arguably more important) component that differentiated Pax Britannica from the Pax Americana was colonies. The US was brought into WWII with an ideological high-mindedness that prevented us from doing what GB/France did in WWI with the Sykes–Picot Agreement and chop up colonies as war proceeds. Those colonies are precisely what kept Britain afloat -- i.e., from Indian spices, Indian silks, and high quality Wootz steel, as well as from rich land - Virginian soil that was ridiculously fertile and prime for tobacco. (All of which had to be routed through GB and taxed, often to return to its origin to be processed, leading to a bunch of pissed-off rich white landed gentry to commit treason.)
I digress. Pax Americana would have occurred regardless of our (overinvolvement) in national affairs. Quite simply, there was no one left with an infrastructure intact post WWII to produce the materials for reconstruction. A well-executed Marshall Plan in place ensured an economically secure US post-WWII, the profits of which allowed a "Leave it to Beaver" suburban (somewhat artificial) saudade. Teamsters needed to load that cargo on and off ships, machinists needed to work the lathes to create those widgets being exported to a reconstructing Belgium. This also was during an era when the highest federal tax rate was 91% rather than 35%, because yes, _wars cost money_. If congress declares a state of war, the executive administration has the moral obligation to the country to increase taxes appropriately (not print 30 year notes like they were going out of fashion, leaving the mess for the next administration / generation to clean up).
Surely, there are people making a net gain off of the security provided by the armed forces. But it's definitely not John in Minnesota working the Bridgeport. Those jobs are all mechanised. The net gain exists is going to someone working logistics in a nice bespoke suit from Saville Row will flying First Club BA from JFK to Heathrow. The profits will then get routed to some holding company that owns the majority stake in some set of Lichtenstein AG's with an executor being some nameless attorney in the Dutch Antilles who isn't allowed to reveal the name of his client.
He'll keep his money there, or maybe move it to UBS if he's accrued enough capital to be invited into the Private Wealth community. Maybe he'll be advised to move that money into a holding corporation based in Hong Kong, buy US 30 year notes and take the small hit on the 11% HK tax and tiny purchasing power loss if the coupons + payout doesn't beat inflation because you'll be claiming the profits at 15% long-term capital gains anyways (and that's if you even want to remit the money back into the US).
(I'm not a tax attorney (especially not one with experience in international tax law), CPA, nor a chartered accountant, but I do enjoy reading technicalities (in any system) because semantics of category is like a game of chess to me. An actual professional will obviously not execute the series of strategies I delineated above in that exact form, but it covers the gist of how Romney had an effective tax rate of 13.9%. For more details, PricewaterCooper has a PDF floating around for corporate tax minimization. Julius Baer, a former private bank for high net-worth individuals, was one of the first major Wikileaks. It delineated the methodologies of legal money movement for individuals and their method de jour at the time (though its an arms race against tax institutions, so they constantly evolve like infectious bacteria vs antibiotics (you pick which is which ;) ))).