First :Crusade does not make only evil but create trade with muslim world. With that we found some Lost greak philosophers. The most important was Platonism and Platon whose was lost for Western world(Western Christianity knew some Philosophers as an aristotle, but some became forgotten. ). In fact, it is the discovery of neoplatonism kick off Renaissance.

Second :between 1150 and 1300 was full blown war between Italian City states and German Emperor. City states won and start not only fighting each others but fight for prestige. With that they funded by Intelligent mens whose have creative minds.

The second Black death of 1348 has literally destroyed 35% of europe's total population. But it also allowed the monopoly of old trading families in Italy to be destroyed, and thus to enrich new families start competing with each other. this allows competition and better life and with that creativity.

The third was the crisis in Christianity due to the Avigion exile. This make Catholic Christianity split in two partsand with this, the Pope was able to compete with himself and sponsor science.Also make Philosophic divide and space for New theological questions. also Catholic Christianity was more liberal to Romano-Greek philosophers ať the time and allowed this.

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