POSTCARD
HISTORY INDEX:

The French law dated November 18, 1903 required that the address side of the postcard be divided into two parts, one for writing a message and one for the address. The two parts needed to be separated by two vertical lines.  The correct use of the card was supported by these printed guidelines:

transformed "Divided" back stamp still on the left side the addres is also written left

On the left side ”Partie réservée à la correspondance  " : the part for writing the message.
On the right side “Adresse du destinataire”: the part for the address.
 

France was one of the first countries to introduce the divided back, thus they set a new regulation in 1904 which required that this phrase be printed on postcards: "tous les pays étranger n'acceptent pas la correspondance au recto (se reinseigner à la poste)" which means : other countries don't allow always the writing on the address side - information in the post office).

At that time, both parts were not equal and the space to write messages was not always big enough, so people continued to write their messages on the picture side. A law dated July 31, 1906 required that the divided back be in two equal parts. It is at this time that the habit of writing the messages on the picture side began to disappear. 

French vintage postcard divided back- not equal parts means 1904 - 1907 period

Finally, in 1907 there was an international postal congress in Rome that regulated the use of the divided back for 45 states, including most European countries. Now it was permitted to write a message on the address side, and a stamp on the address side was required.  In fact, the back side became the front side (picture side) and the front side became the back side (address side). 

In 1910 there was a limitation added in the regulation for the use the printed matter. One was not allowed to write more than 5 words, when using this tariff of 5 cents.

In 1916, during the Great War, paper of minor quality was used to made postcards. Sometimes, these had a green back. The use of the green back was common until 1930. 

*Note: You can not necessarily date a card with a green back to the period from 1916-1930.  This is due the fact that between 1900 and 1904, they also sometimes used green backs although with quality paper.

 It is my experience that you won’t find this green back on a lot on fantasy cards, as they were more likely to use it on French view cards.

In 1917, the postal tariff changed to 15 cents and then in 1920 it increased to 20 cents.