What was the allies unified strategy for winning the war? why did the axis powers fail to develop a unified strategy for winning the war?

The Allies chose to focus on Europe first, the Pacific Theater second. Nazi Germany was seen as the bigger threat. The Axis, on the other hand, were separated by different interests and tactics. Mussolini's adventures in Africa, Hitler's focus on Europe and Russia, and Japan's empire building in the Far East, all of which didn't exactly focus on any one enemy. No one really held the kind of super-conferences that the Allies did to discuss overall wartime strategy. Italy was eventually bullied into assisting Germany, something that the Italians eventually resented Mussolini for.