The 1340s decade ran from January 1, 1340, to December 31, 1349. Events and trends The Black Death spreads across Europe. Before, it had 74 millions inhabitants of the some 442 in the whole world.Growth of power of the Byzantine aristocracy at expenses of the imperial power. 1340 – The Battle of Sluys is fought between the naval fleets of the Kingdom of England and the Kingdom of France. 1342 – The English destroys Genoese galley squadron at Brest; widespread breakdown of order in… (More on 1340s)