During the mid-20th century many Arab leaders and intellectuals made the case that people from Morocco to Yemen were part of one ethnic/national group called "Arabs." This was a new idea. While the term Arab has existed for a long time, for most of history "Arab" only referred to people from the Arab peninsula (sometimes Bedouins and people from other regions who were directly related to Arab colonists/invaders were also referred to as such).

Until the 20th century North Africans, Syrians and Egyptians who lived a sedentary lifestyle generally had a similar relationship to Arab culture that a French or Spanish person would have with Latin in the middle ages. They learned classical Arabic if they were educated, respected Arabic literature and religion but considered themselves separate people. Egyptian Arabic is as different from Classical Arabic as French is from Latin and North African dialects are much more different. To this day if you hear an Egyptian casually use the word "Arab" they usually are referring to someone from the Arab peninsula.

During the rise of nationalism in the middle east during the waning days of the Ottoman empire truly nationalist movements which wanted to set up separate nation states in separate regions competed with pan-Arab movements. During the Mid-20th century Pan-Arabism became very popular and was spearheaded by people like Qaddafi and Nasser. These ideas were popular because there was a hope that Arabs could compete with the west if they were united and also because they hearkened back to the glory days of the early Caliphs, however they proved to be unworkable.

The Federation of Arab Republics and United Arab Republic (which were the two main Pan-Arab experiments) failed for a number of reasons. First of all Libya, Egypt and Syria are each vastly different countries with vastly different languages, cultures and economies. Many common Egyptians would have trouble completely understanding a Syrian, and Libyan is basically incomprehensible to Syrians and Egyptians. While it's possible to create a national identity without a shared common language, it's very difficult.

The cultural, tribal and political differences were especially important because Arab states are generally very weak and tend to rely heavily on family, community and tribal connections to rule. This leads to a system that is suspicious of outsiders, and means that people who aren't from the same area, tribe or even family of the ruler are often shut out of power.

This dynamic meant that the respective ruling classes in Libya, Egypt and Syria distrusted each other almost from the beginning and were not able to successfully coordinate with one another. This mutual distrust and unwillingness to share power led to the demise of the pan-Arab experiments and is also the major cause of the violence we are seeing today in the Arab world.