Is that all? How in the first place did it come to a point that the Americans can just print the US dollar for the World? Ah I forgot, the World was held at gun point by American cowboys...
How many wars did canada and australia wage on the 'rogue' countries like USA?
USA of the yester years improvised from the mistakes of UK. Instead of occupying the countries like UK, it went in and fought wars with several countries which doesn't favor US. If it succeeds, it will control the country. Else, it will use CIA covert ops to change unfavorable regimes and make them puppets. Once the number becomes significant, getting dollar to be a reserve currency is no big deal. Also, having a huge war industry that it can control at will does matter a lot. When the major world wars happened, US did sell a lot of supplies and didn't participate in the war until it was bombed. Enter the war at the final stage, flash a couple of nuclear bombs and the rest of the world falls in line. Countries also fall in line.. not just people. By that time, every other country got it's resources exhausted.
USA of today is not that smart. With the fall of USSR, the seeds of the fall of US are sown. If not today, it will happen shortly. It can be postponed a little while but can't be avoided. By the way, look at the trend of Australian dollar. It gained a lot of value in the recent times.