Circuses used to be a really exciting form of entertainment.
They were often the only chance for people to see exotic animals, and the tricks really amazed the crowds. Once we started to become concerned with how the animals were treated, however, perspectives changed. We realized that these wild animals shouldn't be kept in such horrible conditions and forced to perform for us.
In addition to harming the welfare of the animals, keeping these wild beasts confined can be dangerous for humans, too. There have been numerous documented incidents involving circus animals attacking humans, and horrifying footage is now showing yet another tiger attack during a live circus show in China.