Here's a little more backstory and setting info based more off what I remember than what's in that link...
The start of the superheroic age basically began back in the early century with 'pulp comic' style vigilantes - basically normal people with gadgets, special training, or what have you. There were few real organizations, hero or villain. Statesman/Marcus Cole was one of the original heroes as was Lord Recluse (or at least, the two were operating back then as adventurers).
The emergence of superpowers was probably tied or at least timed with the opening of Pandora's Box - when Statesman and Lord Recluse opened the box, they received their powers and released... well, lots of stuff! Functionally, this was equal to the Golden and Silver Age of Comics and early organizations were formed or would have its roots here (like the Midnight Club). Likewise, many current heroes or their predecessors (like Manticore) would also begin operation at this time.
The Modern Age begins with the discovery of dimensional portals and Portal Corp. It was the portals that would cause (and allow) the Rikti to attack Earth and destroy most existing superheroes and organizations. The Surviving Eight (Statesman, Manticore, Sister Psyche, Positron, Back Alley Brawler, and a few others) would be the only older generation of heroes to survive. They would also serve as the backbone for the new incarnation of the Freedom Phalanx.
The Rikti War would end (or at least, dwindle) when Omega Team (composed of a handful of very tough heroes lead by Hero1, Great Britains premier hero) carried a nuke through one of the Rikti Portals and detonated such as to destroy the ability of the Rikti to portal in reinforcements. As this was a suicide mission, Alpha Team (composed of most of the remaining superheroic forces, lead by Statesman) provided a distraction while Omega Team did their thing - both teams took heavy losses with Omega Team lost completely (even if they survived, they wouldn't have been able to get back through a portal). In honor of Omega Team's sacrifice, heroes are not allowed to wear capes until they have earned the right.
The aftermath of the war saw the rise of Vanguard, dedicated to the control and security of Rikti and portal technology. Longbow came in to existence a few months after, secretly backed by Manticore to do what he felt the Freedom Phalanx would or could not.
Hero Corps would gain a lot of influence - while existing previously, with the shortage of superheroes and the remains of both Rikti and villains looking to get some in the power vacuum, they became a much needed organization, if a little mercenary.
The War Walls subdivided Paragon City into sections. Between and outside them were either unrecovered ruins of the city or simply the outside world. They had been erected by the Rikti to cordon off defenders.
Superheroes are required to register with the city in order to operate and generally will work under the auspice of an appropriate department (MAGI for magic-based heroes for instance); this is part of a law (don't remember the name) to allow (rather than restrict) heroes to operate interstate and with less red tape as well as limited ability to work abroad. Revealing of secret identities is not required through such information is required to be given to the supervising heroic organization. This is essentially the only regulation that superheroes have - by registering, they are basically granted federal rights as law enforcers as well as special forces (to deal with things like Hamidon) with the capability to do most anything required within the US (along with receiving benefits like free medical care). They work in tandem with the police (both normal and superpowered police forces). Other major cities and countries may operate differently, but most will probably have at least similar environments (War Walls, etc). Within Paragon, there remains Rikti forces in the sewer system, cavern network, and what have you, along with other villainous groups as well as various sections of the city that are still outright dangerous and designated as Security zones.
Superheroes and police act pretty co-operatively and share an amicable relationship; the police provide manpower that superheroes usually do not have and support or lead superheroes as needed. Police in Paragon are a bit more military than modern day ones mostly because of the still dangerous situation - they provide security at security checkpoints, take on the everyday superpowered situations when heroes aren't around (and help when they are) via training, super suits, robots and superheroes who are actual law enforcement (such as Coyote), and what not.
The Rogue Isles is the polar opposite of Paragon. It's ruled by Lord Recluse and the Arachnos organization. It is a sovereign nation recognized by the UN though as it is composed of entirely villains and criminals, it's a reluctant recognition. Recluse doesn't care what goes on and anyone may come and go freely (which means it's a good place for nations to do... less than legal business, likely one of many factors that allow the Rogue Isles to exist within the UN)... so long as it doesn't interfere with Arachnos business. Though that doesn't mean that Arachnos doesn't in-fight (something Recluse encourages as he believes in survival of the fittest both in Arachnos and on the Isles). The various Isles are 'governed' by high ranking Arachnos leaders - Black Scorpion, Ghost Widow, Captain Mako, Scirrocco, and one other person. Any other rules are enforced only by the person making them though there are many not working for Arachnos that hold considerable power so those that don't respect the pecking order (or aren't powerful enough to defy it) generally don't last too long while those that work within the rules generally are successful.
Since the Isles are recognized by the UN and technically they haven't done anything wrong (Arachnos isn't the one that does most of the illegal stuff on the isles and they do operate a security force to 'police' the place), the Isles is basically at peace (technically speaking) with everyone. However, Arachnos nevertheless has operations in Paragon and elsewhere and likewise, Statesman leads an unofficial 'war' in the Isles along with Longbow.
Lastly, there's also Pocket D (not sure if ZK will include this). It's basically a pocket dimension run by the DJ. Within the boundaries of Pocket D, the DJ is God. What he says, is. Which means it's neutral ground with no fighting as it's first rule - it's common to see say... an Arachnos Widow talking to a Freakshow. The pocket dimension doesn't exist in any one spot - the DJ can link any door in the 'real' world to any entrance in Pocket D and usually changes them as desired or needed. He really has no enemies save for a portal hopping Redcap. It's also home to an alternate dimensional version or the spirit of (it's not clear) of War Witch.
Phew... there's a lot of smaller details too that are worth mentioning but that's another story.
Edit: Oh, one origin specific detail is that all magic-users can do magic from having the blood of the Mu civilization. Thus, all magic users either need to be descended from them, come from somewhere off-Earth, possess a Mu artifact, or gain their innate magical powers via some other event (gift from a god or what not).