The modern animal welfare movement emerged in the 19th century, with the establishment of organizations such as the Royal Society for the Prevention of Cruelty to Animals (RSPCA) in England. However, it wasn't until the 1960s and 1970s that the animal rights movement gained momentum, with the publication of influential books such as Peter Singer's "Animal Liberation" (1975) and Tom Regan's "The Case for Animal Rights" (1983).