WWII

 The second world war was a period with many battles and death people. Nazis killed a lot of Jews and experimented with people. This was a terrible way of discovering new medicines but thanks to this we made many advances.
ALTERNATIVE VERSION.
 If Hitler hadn´t started the WWII many advances wouldn´t have existed like new medicines or those laws against the animal mistreatment. However, it was a terrible war and this kind of racism should have never existed so in my opinion, wars shouldn´t exist.