Dragon Curfew

The Dragon Curfew was a forceful curfew enacted in Dragon Town, a district of Fillydelphia that housed a seemingly exclusive populace.

Fillydelphia Fires
It was unclear of Equestria's past run-ins with Dragons, such as the incident with Razer had anything to do with the stigma that was faced in Fillydelphia or not. The first known incidents involving the Fillydelphia Police Department to grow distrusting of dragons happened during the Fillydelphia Fires, a series of assumed-arson fires that endangered the populace. The police department pinned the blame the dragons on these fires, and thus, dragons were judged entirely on their species, rather than their actions.

The department enlisted the aid of, who in-turn enlisted the help of to deal with these issues. Spike, who was already biased towards dragons due to an incident involving the dragon thug, was conflicted during the investigation, but realized that not all dragons were evil when he came in contact with the geeky shopkeeper of Dragon Comics, Mina, who snapped him out of his bigoted beliefs and showed him dragons were every bit as capable of love and kindness as ponies.

With his confidence in dragons restored, Spike told the police chief that he believed the dragons were innocent, but the chief did not believe him, and thus, the curfew was forced upon the dragon populace.

Curfew
Spike ran to see Mina, now apart of a small of dragons and protesting the event, confused why it came to this. Mina told Spike that she knew he wasn't a quitter, and Spike went to try to find the true culprit of the fires. During his investigation, Spike came across a Fire Snail who was accidentally creating the fires blamed on the dragons. With this information, the police department freed the dragons and lifted their curfew.

Behind the scenes
It doesn't take much insight to see the real-world parallels of the curfew and race relations in the United States of America. At the time of release, was a controversial issue for many reasons, one of which that it was too 'political' for the series, as it featured a fairly realistic portrayal of institutionalized racism, despite its happy ending.