The first "passports" were letters from rulers announcing the presence of ambassadors, mess angers, or well off people. Since linguistic and ethnic boundaries were high very few people left their little chieftains so the letters were rare. The Bible mentions such a case in the Old Testament where a letter was used by an emissary.
Passports in a book form came into being during the rise from the Dark Age in Europe. Travellers, mostly merchants, had to have papers allowing them access to various city-states. The system held until the European industrial revolution and the more importantly the advent of trains. Railroads made paperwork unduly and the fact only the rich travelled lessened the need.
World War I though destroyed the globalized world and passports returned. After World War II the middle class began to travel and more passports were used as a result. Today, the United Nations' International Civil Aviation Organization governs passport standards. Their oversight reflects the importance of airways in international travel.
Passports can be a sensitive subject. Having one is considered proof of citizenship. The majority of South Ossetians and Abkhazians have Russian passports and Russian leadership has stated it will protect those who have their passports both inside and outside the Russian Federation. Similar situations exist in both Moldova's Transnistria and Ukraine's Crimea.