Modern day greed started when success became as a sign of self worth, and people started to view themselves through other's eyes. This self conciousness was aided by television. TV commercials always showed people painfully aware of themselves, and made the viewer into those people. Also when people have equal opportunity, as in this country, they don't have a lot of excuses for not succeeding. They can't say that they are stuck in the peasant class. The connection between success and worthiness seems a lot stronger in this case.
The other thing is that success (self-worth) is defined by how much money and toys you have. The toys are especially important because you can put them on display and everyone can see them. I think greed really kicked in after WWII when we became an amphetamine fueled consumer society and people were working like good little gerbils on the treadmill so that they could have lot's of money to buy toys and make the Joneses envious. Of course if the treadmill didn't pay out enough, you could always finance your toys through debt. Just look at how many people have Kitchen Aid mixers they've bought on credit that they never use.
