1930's: As far as I know, the only kind of media that remotely resembled what we have today were Pulp novels and newspaper comic strips. The early precursor to comic books came when one publisher came up with the idea to reprint their comic strips in a collected edition. These had the same look as the comics we have today but were still just the reused strips from the papers. Later on another publisher decided that they could print new material in this form, and thus the medium of comic books was born. Then, in 1939, the begining of what we now refer to as comic books (but should really be refered to as superhero comics) happened, Action Comics #1 was published starring Superman. The golden age of comics began.
1940's: Because of the success of Action Comics, this decade saw a boom in the creation of other superheros. Guys like Batman, Green Lantern, Dr. Fate, the JSA, Captain America, The original Human Torch, Sub-Mariner, and many others that didn't survive. Comic books became the new thing that everyone wanted a piece of. Because fo the war, many people wanted to have heroes to look to for hope. It was a great time for comics and comic book writers and artists. New genres of comics were being made as well which lead to the dark time in comic book history.
1950's: Horror and crimes comics were popular near the end of the previous decade and at the begining of this one. This caught the eye of parents and other stuck up adults. They saw the gore and realism of these books and denounced all books. The government got involved and a man by the name of Fredric Wertham, a psychologist, began his campagn to rid the world of such bad influences. Before the government could do anything, the industry conceded and created the Comics Code Authority. Most comic companies joined the CCA, others just died out. The CCA created rules that made most of the crime and horror comics unpublishable, and made the superhero comics dull. Most fo the heroes from the 40's didn't make it through this time due to the reduction in interest caused by the senate hearings. It took a while but gifted writers came along and revitalized the industry. According to my source, the first silver age comic was also the first appearance of the second Flash in 1956. I think others came along near the end of the decade and the industry made it through.
1960's: This was the second boom for the industry. Marvel and DC began to create the majority of the most popular characters in all of comicdom. Here is where most people probably got on, mainly because it had been a long time since the 40's but also because things were wicked.
1970's: A lot of experimenting went on. Sci-fi, romance, and comedy comics were published. Popular movies and tv shows were made into comics as well. The existing comic characters went on with their lives, I don't think too many cool things happened in the industry. Nothing really memorable anyway.
1980's: This is what I consider to be the best time in comics. Big events marked the decade: Crisis on Infinite Earths, Secret Wars I&II, The Dark Knight Returns, The Watchmen, and many others. This is when the industry saw how mundane it had become in the 70's and therefore did something about. Some of the best artists and writers that we enjoy now became famous during this time. The classics of the industry were written in this time period. The trend of renovating the industry did lead to something that I (and it seems other fans in general) found unsavory. The comics of this era followed the trend refered to as "grim and gritty". Frank Miller's run on Daredevil is the begining of this. Miller's realism and darkness took Daredevil from his second tier status as a spiderman clone and made him his own character. His work made sense. The imitators used the gritty-ness in more of a sensational way. It was "cool" to see this dark heroes bending the rules or walk the fine line of good and bad. This lead into the next decade.
1990's: I am surprised the industry lasted through this time. It sucked. I was around to see it so I know for sure. The rise of the anti-hero. Damn them for destorying the industry. Flashy gimmicks were valued over stories. They did things like make guys like Wolverine and Punisher kill the bad guys and make it acceptable, kill off Superman as an attention grabber, Spiderman's clone saga, and made Hal Jordan go nuts. The X-men BECAME the marvel universe, while the others were sent to another universe because no one cared. Near the end they tried to fix things but the crap stuck to the bowl. Luckily we still had some hidden gems to hold on to. The major culprit was Image comics, whose characters were created from a cool sketch first and believeable story last. Things seemed to have readjusted near the end though.
2000's: It is only 2004, so don't take this as certain but I would like to guess at how thigns will turn out based on what I see right now. I haven't heard of many new characters being created. I see some of the mistakes of the past being fixed, at least at DC. Hal Jordan will be returning in a few months. The second Hourman may be killed off (I don't know yet, I haven't picked up the issue), although he wasn't a mistake in my opinion. Just a lot of reboots happening now. I also see a lot of changes based on the recent interest in comics from the general public because of the frequency of comics based movies. Changes in rosters because certain characters were on the cartoon (ex: JLA dropping Kyle for John). This isn't a bad thing per se but in the case of the example, I liked Kyle better. There haven't any major crossovers lately, the kind of event that I loved during the eighties.
If anything here is wrong or you have anything to add, please email me and I will add your comments. If I remember this article, I will keep my own history. If not then it probaby means that I lost interest in the medium, that would also mean the comics really suck because I can't imagine not reading comics any more.