Philosophers generally agree that, not one man changes the world. That change is inevitable and people choose the leader that offers them that change when the time comes. In recent times there have been many leaders who have offered change but few have delivered and the ones who do bring real change get quickly eliminated.  

This might be because while the populace asks for change, they at the same time resist it. So the effect is negated. However, when a people become hungry and fall on hard times, the leader no matter the means, who promises and delivers prosperity is quickly embraced. Most of us are familiar with the story of Jesus turning water into wine, one loaf of bread to dozens and a few fish to many hundreds. This is precisely what Hitler did for his people and they embraced him, in fact many people the world over admired his ideas and tried to emulate him.

But in philosophical terms neither Hitler or Jesus really changed the world, they were simply leaders of convenience and opportunity that filled a void at critical time points in history. 

So what if Hitler eventually took control of the world? Where would we be today? The most diabolical of his ideas was human genetics and the eliminating of weaker species through eugenics, sterilization and killing. At the time, a widely accepted solution to many problems that plagued the world, in fact it was most popular in the US with many experiments being carried out. In the end, those ideas only became rejected because Germany lost the war and anything connected to his ideology was quickly demonified.

If Hitler won the war there might have been  less people suffering from genetic disease  and a few million less Jews and possibly some massacres in Africa for some time. As the world would eventually adjust to his rule and those that would follow, it is completely possible that as peoples bellies grew full and hope was restored to them, that eventually the modern world would have become exactly as it is today, with some possible meaningless modifications.