The History of Amendments to the US Constitution

In America, passing an amendment to the U.S. Constitution is quite an undertaking. It's only happened 27 times in the last 235 years. The process that's actually been used involves the following. You need to get two-thirds of the US House of Representatives and three-quarters of state legislatures to ratify it. If you call a new convention, it could do anything - scrap the whole Constitution and write something completely different.