The British kept their financial house in order! Only in WW1 did they end up spending all their money, cashing in all their chips, and becoming indebted to the US and on the hook for bad debts. In WW1 they had no choice.
In the US the British did not allow the Americans to produce certain goods (you Americans probably know a lot more about this than me, I have a feeling they limited printing presses or something like that).
India was able to pay for a lot of British troops and supply lots of Indian Army soldiers. The British supressed Indian manufacturing so India became a net importer of textiles.
When the British had a trade deficit with China (ie China had lots of stuff to sell but only really wanted gold). The British sold them opium and got HK in the war. Britain had to adapt.
These types of economic warfare doesnt seem viable today as the war will be more expensive than any benefits.
The US has to adapt today, they need to cut spending, get their fiscal house in order, and encourage savings at the national and family level. They can still expand their military but have to do it in a smart manner. Expensive projects NEVER seem to be cut. Rumsfeld cut what, one program, the future artillery something, in his time as defense secretary.
The US economic situation worries me far more than any future peer competitor. In Iraq they wanted (and prepared for) an Ashanti campaign and they got a Boer War.
The US is much more dominated in the Naval field than the British ever was. Would it really hurt to shift some of that funding into a larger and better equipped army?