Of course, we can never be sure about what might have happened if things had been different. However, we might imagine that WWI would not have happened if Bismarck had not been dismissed and Kaiser Wilhelm II had not taken more control over Germany's foreign affairs.
The thinking here is that Bismarck could have restrained the Kaiser's desire for Germany's "place in the sun." Bismarck's policy had been to try to avoid any actions that would really scare France or Britain. He did not want them to see Germany as a threat. By contrast, the Kaiser wanted Germany to pursue power vigorously. When the Kaiser took over, he took actions that made Germany seem like a threat. Because of this, Britain and France (especially) got worried and started to think about war. This meant that war was much more likely to happen if anything came about to set it off.
So, if Bismarck had been able to keep Germany on a less aggressive path, WWI might not have happened, Hitler might not have come to power after WWI, and WWII and the Holocaust might not have happened. Of course, there is no way to know for sure...