Did us emerge as a developing world power after world war 2?

Yes. Before the war, the U.S. was a world power but the superpower of the time was arguably Great Britain with a global empire upon which "the sun never set." Of all the combatants in World War II, the U.S. suffered little or no war damage (apart from a Japanese balloon attack in the Pacific Northweat which did little damage). Hawaii was not yet a state so the Pearl Harbor attack doesn't "count." The only American territory occupied by a foreign army was an island in the Aleutians, which the Japanese seized hoping to lure the American fleet north. The U.S. didn't take the bait but let the Japanese have the island (which was ultimately recaptured). With the country intact and the economy thriving, the U.S. emerged as the dominant postwar power. And for a time, it enjoyed a nuclear monopoly, giving it extra clout. Britain, on the other hand, had been devastated by constant air attacks, and after the war it was a shadow of its former self as its vast empire began to disintegrate.