World war i was also called because of the millions of casualties and the sheer brutal violence.

  It was also called the Great War.  

Explanation:

  Before that, the world had never seen a war with such tremendous losses and devastation. People from that time believed that there was never going to be a battle like that again. They, of course, were wrong because one decade after World War II began.

not sure maybe the subject closer to it or subject-verb agreement