England was broke at the end of WW2, but not at the start. We had not fully recovered from the cost of WW1 which was only a few years previously but were far from broke, and had been misled into disarming until almost too late. Hitler didn't lose the Battle of Britain, he just stopped it despite his generals' advice that they were on the point of winning.
As to what would have happened if Britain had been defeated it is clearly surmise, but a number of strategists who have written on the subject believe that trapped between NAZI Europe on the east and Japan on the west America would have been in difficulties. And there is no doubt that Germany had the ability to cross the Atlantic in force. No, I don't know what would have happened, but I believe it is likely things wouldn't have gone too well for the USA, and indeed the whole of the free world.