There were many significant turning points in ww2, within which, had they not happened as they did the outcome of the war could, arguably, have been very different.
In particular the attacks on Pearl Harbour, as they changed the whole face of the war. If the Japanese had not attacked Pearl Harbour in 1941, then the war in the Pacific may have never escalated to the use of nuclear war fare.
It is important to note however, it can also be argued that the dropping of the atomic bombs was the biggest turning point of the war. This can be inferred as it ultimately changed modern war fare forever.
Despite this, if the Japanese hadn't attacked Pearl Harbour they may have never provoked the USA
to use nuclear weapons. The use of nuclear weapons acted as a symbol of the American power, and if they hadn't angered the USA than they may not have been as hungry for being creditable for the end of the war with Japan. This is shown by the Soviet army having enough power and hold over the Japanese to have been able to defeat them, without the need of nuclear weapons.
To conclude, the attacks on Pearl Harbour was one of the biggest turning points of the war, as it sparked the conflict and tension between the USA and Japan. This conflict ultimately led to the abrupt end to the war in the pacific.