The correct answer is 4) when Germany attacked Russia and Austria-Hungary invaded France.
The first major battles of World War 1 occurred when Germany attacked Russia and Austria-Hungary invaded France. We are talking about the Battle of Tannenberg of August 26-30, 1914, at the very beginning of World War 1. It was held in East Prussia, modern-day Poland. The German troops attacked and defeated the Russian Army. The second major battle was the Battle of the Marne from September 6 to 14, 1914, held at Marne River in the East of Paris, France.
