Why don't the Arab World and the Spanish World each form just one nation instead of dozens of them?

Do you mean the way that the USA and Canada have done?

"Balkanization or balkanisation is a geopolitical term originally used to describe the process of fragmentation or division of a region or state into smaller regions or states that are often hostile or non-cooperative with each other.
The term has arisen from the conflicts in the 20th century Balkans. While what is now termed Balkanization has occurred throughout history, the term originally described the creation of smaller, ethnically diverse states following the breakup of the Ottoman Empire after World War I"
Source and further information:
http://en.wikipedia.org/wiki/Balkanization

Corruption, persecution, no freedom, etc. led to the many spanish colonies to separate.

The British formed the Arab world as we know it today after World War 1.

there are many areas that are predominantly english-speaking as well and the number is constantly growing as countries see it necessary to educate their citizens in this common launguage. english is the third most popularly spoken language in the world, topping arabic. chinese is the most common (obviously due to population numbers), spanish second, then english. should we consider ourselves part of an english "world?" i say, the more languages spread, the better. the more prevelant a language is, the more likely we are to pick it up and learn to communicate with our worldly neighbors!!