Spoilers,
Red Arrow and Green Arrow give some backstory on how E-2 citizens arrived to main Earth. Some of it was shown in the preview.
Basically they were followed by Apokolips forces. Ship with most of the E-2 heroes stayed behind to hold them back while ships with mostly citizens and Superhero "shepherds" (Red Arrow and Terrific were mentioned) went straight to Earth.
At the end E-2 heroes were overwhelmed and initiated self-destruct of the ship taking out most of the Apokolips forces.
Civilians and Parademons landed on Earth, obviously big fight started. Teen Titans were first to help out E-2 survivors, we know how that ended for them. We also see a scene where Red Arrow saves Red Robin as mentioned in earlier issue.
Even with most of the Apokolips forces dying due to explosion of the E-2 ship it seams that enough survived to give a serious fight for Earth since war lasted multiple weeks.
After it ended millions of E-2 people were left homeless. Main earth citizens became paranoid and Global Peace Agency was formed that tried to "help" by basically giving out earth-cards and stuff like that. We can see how that turned out.
GA tried to help with making Seattle "card-free" zone and using his family wealth to build shelters and stuff like that.
At some point GA met RA and they realized that someone was capturing E-2 heroes.
Looking for more info they found out that Maxwell Payne fucked up Earth's planetary defense codes days before arrival of E-2 and that during self-destruction of E-2 heroes ship Brother Eye satellite discharged lots of energy.
They managed to access Eye's archives and found out that Brother Eye managed to teleport away heroes before ship went kaboom. Heroes thinking that Brother Eye works with Apokolips (due to similar technology) fucked up his satellite and eventually they were taken in by Cadmus... somehow.
GA faked his death to get rid of Deathstroke/Sue trailing him and with "Queen drones" managed to locate island where they were being kept.
Not much happened in this issue but it filled up lots of blank spots and whole backstory is kinda clear now.