Prawer was part of a cadre of historians, including
Claude Cahen and Jean Richard, who freed crusader studies from the old conception of crusader society as an exemplar of pure, unchanging
feudalism that spontaneously emerged from the conquest. This view, which originated with feudal
jurists in the
thirteenth century, was held to by modern historians since the early thirties. Through the work of Prawer, particularly his two papers from the fifties, and his colleagues, crusader society began to be seen as dynamic, with the
nobility gradually putting checks on the
monarchy. The combined efforts of these historians led to a surge of new research into crusader society. Prawer's research extended to a wide variety of other aspects of the crusader states. Among the topics he addressed were
land development projects and urban settlement, agriculture, the Italian quarters of port cities, the types of
landed property, and legal issues in the
Assises des Bourgeois.
One of Prawer's best known works is the
Histoire du Royaume Latin de Jérusalem, which won
him the Prix Gustave Schlumberger of the
Académie des Inscriptions et Belles-Lettres. The two-volume work presents the
crusader states as a working immigrant society, and shows the importance of
immigration and
labor shortages. Another book by Prawer,
The Latin Kingdom of Jerusalem: European Colonialism in the Middle Ages, which was intended for a larger audience, was more controversial. In it, he portrays the crusaders as a society of
Frankish immigrants living in complete political and social segregation from the local
Muslim and
Syro-Christian population, and terms this phenomenon "
Apartheid". To Prawer, it is the settlers' refusal to
assimilate and their reconstruction of a European-type society on foreign soil, as well as the persistence of indigenous institutions without any interference, that mark the Crusader settlement as
colonialist. His thesis is that the economy, society, and institutions of the Latin states are best understood in the light of their colonial status. The 1980 book
Crusader Institutions collected a number of his earlier publications and expanded upon them with revisions and new chapters. The book continues his treatment of the
Kingdom of Jerusalem as a European colonial product but focuses attention on five topical areas, while throughout employing the tools of
textual criticism and commentary on sources. Especially prominent is his coverage of the status and administrative role of
burgesses, which had not received such attention before. In his last years, he published a book on a topic of especial interest to him,
The History of the Jews in the Latin Kingdom of Jerusalem, which examined the tightly-knit isolated Jewish communities of the
Levant, the
Jewish philosophical feuds they engaged in, and their dreams of
restoring Israel.