Learning history means you get to know the events that helped the shaping of our world. Some say that everything happens for a reason, and why wouldn't that be? I think the most important reason to learn our history, is to recognize certain patterns. Analyzing these patterns could help is to prevent some historical events from happening again.
Take in mind some deceases that took a massive amount of lives. Have a look at the "Black Death". The bacterium Yersinia pestis caused several plagues, these plagues went out to reduce the world population from an estimated 450 million down to 350 million in the 14th century.
From world pandemics like this one, we've learned. We got to care more about personal hygiene and developed medicine.
World wars not only shaped the world, it has changed our mindsets as well. We've learned from it, but the world balances have changed. The relationship between the United States and Russia is still not great. The outcome of the war had major consequences for all parties involved. Germany paid off its debt in 2010, that's only 8 years ago, and 99 years since WW1 ended