which groups were the first to fight in it?
The European Axis powers and the British Empire
World War II
Following the onset of campaigns in North Africa and East Africa, and the Fall of France in mid-1940, the war continued primarily between the European Axis powers and the British Empire, with war in the Balkans, the aerial Battle of Britain, the Blitz, and the Battle of the Atlantic. 
what is montana-class battleship? A class of battleships can you specifically name a few battleships that come under that class? USS "Ohio", USS "Maine", USS "New Hampshire" which company built this class? The United States Navy which wars did such class of warships participated in? World War II what were the typical armaments found in such a class? An increase in the number of primary guns and more potent secondary guns for use against enemy surface ships and aircraft. with reference to the war mentioned previously, which year did the war first begin? 1 September 1939
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World War II [SEP] Introduction
Under the Molotov–Ribbentrop Pact of August 1939, Germany and the Soviet Union partitioned and annexed territories of their European neighbours: Poland, Finland, Romania and the Baltic states. Following the onset of campaigns in North Africa and East Africa, and the Fall of France in mid-1940, the war continued primarily between the European Axis powers and the British Empire, with war in the Balkans, the aerial Battle of Britain, the Blitz, and the Battle of the Atlantic. On 22 June 1941, Germany led the European Axis powers in an invasion of the Soviet Union, opening the largest land theatre of war in history and trapping the Axis, crucially the German Wehrmacht, in a war of attrition.