Answer:
Extreme nationalism was the main scourge of the first half of the 20th century. European countries had entered into a spiral of ethnic, nationalist and imperialist violence since the mid-19th century. This caused that at the beginning of the 20th century, several nations had hardships and rivalries among themselves, caused by territorial factors and political power.
The first outbreak of this situation occurred in the colonialist race in Africa and Asia that the main European powers had in the late 1800s.
But the first situation of gravity occurred only in 1914, with the outbreak of the First World War, which faced the great powers of the time in an unprecedented conflict that lasted 4 years.
In turn, this situation ended up being almost a skirmish when 20 years later World War II broke out, largely caused by nationalist regrowths as a result of the conditions in which the war was over, especially in Germany.
Nationalism ended up costing, in half a century, more than 100 million lives, adding the world wars with the different conflicts that developed before and after them.
