This question, of course, is entirely a matter of opinion. Many would say that, at least in Europe, Adolf Hitler was the bad guy of the 20th century. Encouraging the rise of Nazism and sending many Jews to concentration camps, he advocated the expansion of the Aryan race and condemned those who were different to exile from society and, sometimes, even death.
This is, of course, a question concerning opinion. In European history, some would argue that Catherine de Medici was the bad guy of the 16th century. She basically launched the St. Bartholomew's Day Massacre, which killed thousands of Huguenots (French Protestants).
The similarities between the 20th and 21st centuries lie in innovations. The 20th and 21st centuries have been periods of great strides in technology and other areas.
Radio was not an important invention in the early 20th century. Instead it was developed by Heinrich Hertz in the 18th century. The cotton gin (APEX)
17
: The first Kodak camera
Pretty Bad!
Last-year's smart guy
Fuzzy Door Productions & 20th Century Fox Television
20th century
in the 20th century in the 20th century
1966 was in the 20th century.
The 20th century is the most diverse classical music period.
What was the era in 1912?
He was born in 1869, which was the 19th century, and died in 1948, which was in the 20th century.
20th century Astronaut living in the 25th century?
3901
he wrote in the 20th century