I actually read a very interesting article in USA Today a while back that chronicled the history of the Nigerian scams. Apparently, there were much better employment opportunities in Lagos (the capital city) back during the 70's & 80's as a result of the Cold War. When all that ended and there was no more US & Soviet money flowing in, a lot of educated folks didn't have any way to use their education. Many of them, rather than turning to honest professions like teaching or taking up legal entrepreneurial ventures, instead turned to crime in the form of scams.
Now, this was before the World Wide Web, so most of their scams were by snail-mail, with a smattering of telephone work as well. A lot of these scams involved getting people to physically go to Nigeria. One guy, an ex-policeman and P.I. of all things, was fooled into bringing $20,000 to Lagos to bail some rich, innocent enemy of the state out of jail, supposedly in exchange for something like $1 million. He flew into Lagos, bailed the guy out with the 20 grand, and then they took him to the guy's mansion to give him his reward. But when the got there they just ran into the house and locked the door. Dude was stuck in Lagos minus his $20,000 in savings. And since everybody around had an AK-47, there wasn't a thing he could do about it, either.
Anyway, with the advent of email it all really took off. Since you can send the emails for free, it's totally fine if you only get 1 in a million to produce results. Now they've got thousands of different variations of their scams, and every day a new sucker goes online and buys it, while the rest of us are hitting the delete key and configuring out spam filters.
I can tell you this: I'm not planning on booking any vacations to Nigeria.