The tradition of Halloween was carried to America by the immigrating Europeans. Some of the traditions changed a little, though. For example, on Halloween in Europe some people would carry lanterns made from turnips. In America, pumpkins were more common. So people began putting candles inside them and using them as lanterns. That is why you see Jack o lanterns today.
The origin of the festival is disputed, and there are both pagan and Christian practices that have evolved into what Halloween is like today.
Costumes became more adventurous - in Victorian ages, they were influenced by gothic themes in literature, and dressed as bats and ghosts or what seemed exotic, such as an Egyptian pharoah. Later, costumes became influenced by pop culture, and became more sexualised in the 1970s.