The Gutenberg Press Changes Everything
The actual date varies as to when Johannes Gutenberg introduces his printing press. He has been experimenting for a few years now, but what makes his press unique is the moveable type. Rows of characters are placed into wooden forms BACKWARDS and rolled with a thick ink. The wooden form is then pressed against the paper... thus is born the printing press. It will change everything. Most books are printed by hand with some printing being done with carved wooden blocks. While Gutenberg is limited to printing one page at a time, he can print quite a number of the same page and do so quickly. Bulk printing reduces the cost per book so that he can sell more books for less and of better quality. The exception is books with custom art.   
The Beginnings of a Professional Military
Whenever England and France have a long-term truce, LIKE NOW, the knights and infantry are left at loose ends. They make their money by looting. However, during a truce these brigands become a serious threat to the countryside... preying on the locals, setting fire to fields just for the heck of it and knocking off merchant caravans. To solve this problem King Charles the 7th of France has passed the Great Ordinance through the Estates-General (a weak sort of parliament). He levies a tax in order to organize and support a standing army, pay them a living wage and find mercenary jobs for the rest outside of France. It won't solve the brigand problem entirely but over time, it will make a big difference.    
This Year in Wikipedia
Year 1439, Wikipedia.
- Johannes Gutenberg - Wikipedia, 2014 [last update]
- Movable type - Wikipedia, 2014 [last update]
- Printing press: Printing Revolution - Wikipedia, 2014 [last update]
- Amazon Kindle - Wikipedia, 2014 [last update]
- Great Ordinance - Wikipedia, 2014 [last update]
- McCall, Andrew. The Medieval Underworld. H. Hamilton. December 1982. ISBN 9780241100189. p. 129. (BOOK) Quote: "Like the first attempt, in 1439 [...] at stamping out brigandage [...] proved a failure. For although [Charles VII] did eventually succeed in persuading a large number of the brigands [...] to enter the service of German princes who were at war with one another, the brutality of the mercenaries was so indiscriminate, that within a short while the Germans had paid them 100,000 florins to return to France."
- Estates General (France) - Wikipedia, 2014 [last update]
- French Army: Early History - Wikipedia, 2014 [last update]