What if the Lusitania hadn't been sunk?
Of course, there is no way that anyone can answer this question with certainty. There are too many variables that could have affected the way things happened for us to be sure how the “non-sinking” of the Lusitania would have affected history. My own view is that this would not really have changed anything.
The most likely other response to this question would be to say that the US would not have gotten into the war had the Lusitania not been sunk. From this point of view, the sinking, which killed 123 Americans, enraged Americans and made them much more pro-British than they otherwise would have been. This led directly to the US entering WWI.
I do not tend to buy this argument. I think that the US would have entered the war regardless of the fate of this specific ship. The Germans’ unlimited submarine warfare would still have angered Americans. The US would still have had strong economic incentives to side with the Allies. The Zimmermann Telegram would still have caused a strong response in the US. None of this would have changed if the Lusitania had not been attacked.
Perhaps the strongest argument is one about time. If the Lusitania had really been an important turning point, why did the US take so long to get into the war after the sinking? It is hard to argue that an incident in May of 1915 could have been the major turning point that caused the US to declare war on Germany in April of 1917.
For these reasons, I do not think world history would have changed significantly if the Lusitania had not been sunk.