Why are north america and south america considered to have the most diverse societies in the world today?

The reason why North and South American societies are considered to be the most diverse in the world today is because of their History. North America, especially the United States, is an immigrant country, it received thousands of immigrants from very diverse backgrounds in the XIX century: German, Chinese, Italian, Irish, Eastern European, etc. While South America is a mixture of different races: the Spanish conquistadors had children with the native peoples like the Aztecs or the Incas, plus the black slaves that were brought from Africa.

Due to diversity of multiculturalism and diversity, they are considered as more diverse in the society.  

They have more than 560 official languages which are spoken in United States. And there are more than 1000 languages which are spoken in the societies.  

As Americans are cultural and there is on another factor which make them diverse id immigration. So, due to different cultures, casts and languages these societies become more diverse in the whole world.

either b) they were often feared and despised by other native cultures. or

c) their obsession allowed them to coexist with many other native cultures because of their peaceful nature.