I am going to say 1 because it started 2.5 billion years ago and is still hapinung today
The human cost in WWII was over 75 million in total. 40 million civilians were brutally killed due to Genocide, diseases,massacres, mass-bombings, and starvation. The effect on comptempery society allowed the rise of the Soviet Union and the United States. For both their international involvement increased severely.
C. Worshipping more than one God
The unforseen attack on Pearl Harbor...(which led to WWII)