The year 1939 is generally considered the year that World War 2 definitely started. In september Germany with the help of Soviet Union and the Slovak Republic invade Poland. Within days Great Britain, France, India, Australia, New Zealand, South Africa and Canada declare war on Germany. The United States, like Spain, Ireland, Norway, Finland, Sweden and Switzerland decide to declare their neutrality. Within weeks the Germans occupied the Western parts of Poland, while the Soviet Union took hold of the Eastern part.
At the same time, the German Kriegsmarine heads out to sea and starts targeting British ships. The German U boats and Battleships are remarkably successful in the following months, sinking several large ships, like the passenger Ocean liner S.S. Athenia, the British aircraft carrier, H.M.S. Courageous and the armed merchantman H.M.S. Rawalpindi. The first British succes in the sea war is during the battle of the River Plate where British warships trap the German pocket battleship Graf Spee in the harbour of Montevideo, after which the ship is scuttled by its crew.