<P> The behaviour of the Crusaders appalled the Greeks and Muslims, creating a lasting barrier between the Latin world and both the Islamic and Orthodox religions . It was an obstacle to the reunification of the Christian church and created a perception of Westerners as defeated aggressors . </P> <P> Many historians argue that the interaction between the western Christian and Islamic cultures was a significant, ultimately positive, factor in the development of European civilisation and the Renaissance . The many interactions between Europeans and the Islamic world across the entire length of the Mediterranean Sea led to improved perceptions of Islamic culture, but also make it difficult for historians to identify the specific source of various instances of cultural cross-fertilisation . The art and architecture of the Outremer show clear evidence of cultural fusion but it is difficult to track illumination of manuscripts and castle design back to their sources . Textual sources are simpler, and translations made in Antioch are notable but considered secondary in importance to the works emanating from Muslim Spain and the hybrid culture of Sicily . In addition, Muslim libraries contained classical Greek and Roman texts that allowed Europe to rediscover pre-Christian philosophy, science and medicine . </P> <P> Jonathan Riley - Smith considers that much of the popular understanding of the Crusades derives from the novels of Walter Scott and the French histories by Joseph François Michaud . The Crusades provided an enormous amount of source material, stories of heroism, and interest that underpinned growth in medieval literature, romance, and philosophy . </P> <P> Historical parallelism and the tradition of drawing inspiration from the Middle Ages have become keystones of Islamic ideology . Secular Arab Nationalism concentrates on the idea of Western Imperialism . Gamal Abdel Nasser likened himself to Saladin and imperialism to the Crusades . In his History of the Crusades Sa'id Ashur emphasised the similarity between the modern and medieval situation facing Muslims and the need to study the Crusades in depth . Sayyid Qutb declared there was an international Crusader conspiracy . The ideas of Jihad and a long struggle have developed some currency . </P>

Explain how conditions in the late 11th century europe allowed for the crusades to take place