I bet you were wondering when would the word crisis would pop-up, after all this is the DCU! After much thought, you cant delay the Crisis’s from coming up.
We are now entering the 60’s and this far there was already a fairly complex set of universes. Though one might expect the DCU to have been very firmly established in its two universes before getting into major crossover epic events, that is not the case.
The first Crisis, also known as The Crisis in MULTIPLE earths, was the series of events that would mash up the now established two earths in the DCU. Now, oho would have guessed that of all the main characters on the by now pretty extent DCU, the flash would be the one who would have start a crisis?.
On flash 123, 129, 137 we have the fist breach between our two earths. That will be the set up of the next big upcoming event.
Interestingly to note and to have clear.. is that the Earth-Two Heroes have aged. meaning that throughout all the years that silver age comics were published time continued to pass in the Earth two. Now superheroes, have retired and are now reappearing bringing out pure hearted nostalgia. However its interesting to note that This gap between years is filled with a quite interesting story that will be revealed later. The missing years of the JSA are quite something.
These adventures I believe are as good as the silver age gets. They are action packed… and i mean PACKED. There are lots of enemies, plot devices and lots of super hero action.
Having those three comics as basis, The actual crisis would start in CRISIS ON EARTH ONE. Where the JLA and the JSA would meet.
Up to this point all Crisis have a really happy ending, and everything goes back to where it belongs and the earth(s) is safe and sound. In fact the initial crossover stories between the two earth versions of the same hero, would prove to be quite a succes, so with the exception of Superman, Batman and Wonder Woman. The heroes of earth One, would continue to have adventures with their earth Two counterparts.
The stories however, take on a sort of a formula, with the first team up, being rather cordial and friendly and the next one going at each others throats.
Adventures on earth two also continued on their own, tho not in great amount, generally featuring a pairing of superheroes for example Dr. Fate and Hourman and Starman with Black canary.
Finally of speacial interest to us is Green lantern 40, where Hal Jordan meets up with Alan Scott, to face a threat that would have put in danger the entire universe in a scale not seen in a crisis this far. Showcase 56 on the other hand introduces us to the Psycho Pirate.
Recommended buy 
