It all began 2,000 years ago with the Celtics when they had the power over Ireland and northern France. On 1st of May they would celebrate the beginning of the summer and on the 31st of October was the Samhain. They believed that on that day the dead souls would return to the earth, causing trouble and possessing human bodies. To protect the community from them, the druids would light bonfires and perform sacrifices of not only animals but also humans. They also believed that the presence of the lost souls made it easier to predict the future. When the night was over they would relight the fire so that they would remain warm during the winter. As for the rest of the society they would wear costumes to hide from the souls and make them think that they were one of them.
INFLUENCE OF THE ROMAN EMPIRE
When the Roman empire took over in 43 BC they took their festivities of the celebration of the goddess of the fruits and trees, Pomona, and mixed it with the Samhain combining the traditions, and this is how the bobbing for the apples became part of this holiday.
Pope Boniface IV declared, in 609 BC that the 13th of May was the All Martyr's Day, which was a day to pay respect to the memory of the ones who had already died. However, when the 8th century came Pope Gregory decided to change the date and the name of it to 'All Hallows Day' (All Saints' Day) so that the traditions of the Samhain would be assossiated with the church. Due to this, the 31st of October started to be called All Hallows Eve and as the time went by eventually it became Halloween.
In addition to the 1st of November, the church also tried to implement the All Souls' Day on the 2nd of the same month but it didn't succeed.
Trick-or-treating started in the UK.
At first, it was called Mumming and it consisted of the less fortunate people going house to house on the All Souls' Day asking for food, more exactly 'soul cakes', in return they would pray for their dead relatives. This tradition was implemented by the church as well so that people stopped leaving food and wine for the spirits.
In the 1800's it stopped being about ghost stories and witchcraft and the holiday lost its superstition and religious values. Not only children but adults would dress up, play games and go around asking for money and seasonal foods.
When England took over colonies in America they implemented their customs such as Halloween. In the beginning, only southern colonies such as Maryland would celebrate it because of the Protestant church. When this happened a new version of Halloween began because they started to add their own customs to it.
On Hallows Eve the neighbours would get together to tell stories and tales about the people that had already died, dance, sing and just like the druids they tried to read the fortunes of others.
In the first half of the 19th century, it was more popular but it was only in the second half, when millions of Irish migrated to America, that these celebrations started to spread all over the country.
When it got to the 1920's and 1930's the community would get together in civics centres or in schools to commemorate and try to avoid 'tricks' but they didn't manage to stop all of the vandalism that was going on in the streets, such as breaking windows of shops.
Eventually, between that and 1950's they were able to stop that by turning the festivities more for young people and made a turn on trick-or-treat: by providing young children with treats it stopped them playing tricks.
Another change in this decade was caused by the baby boomers and it made the parties move to each other's homes because of the lack of space for the whole community.
By the time it got to the 1970's/1980's young girls or single women would do things such as: standing in front of a mirror in a dark room with only the light of a candle in order to see the face of their future husband, they would also throw apple peels over their shoulder hoping to see their future husband’s initials or even bob for apples at parties because the winner would be the first to marry.