Imperial system and USA

[rado84]

I've always wondered what is the thing/the event in USA's past that made the country to use imperial measurement system? There are only a few countries in the world using the imperial system and I know only 3 - USA, UK and Australia. As far as I know the most countries, like mine, are using the metric system where everything is so much simpler (not to mention easier to remember) - 1 cm is 10 milimeters, 100 cm is 1 meter, 1 km is 1000 meters, 1 kg is 1000 grams and so on.
So far I've learned some of the imperial values, like an inch, a mile, a yard but the lbs gives me a serious headache.
So, do you know what made America to use the imperial system?

I thought to post the topic in "History" but it's not exactly history related, so I decided Off-topic is the better place for it.