We’re living in the most technologically advanced time in human history and most of that technology is used for destructive purposes. War is one them.
Music: Heartbreaking by Kevin MacLeod
Number of soldiers: en.wikipedia.org/wiki/List_of_countries_by_number_of_military_and_paramilitary_personnel
It’s hard to estimate how many soldiers there are in the world (also because not everyone in the military is counted as a soldier). The official number of soldiers worldwide is around 70 million, but with paramilitary (that's non-official but still they are armies) we’re definitely talking over 100 million.
Over 100 million killed in the 20th century alone: en.wikipedia.org/wiki/List_of_wars_by_death_toll
1 billion estimate: nytimes.com/2003/07/06/books/chapters/what-every-person-should-know-about-war.html