This is a bit of a complicated question, while the church SAID that they where trying to reclaim the holy land, but it was actually mostly started for political reasons.
Muslims and Christians actually got along fairly well in the 8th century. But with the Battle of Manzikert, the tension increased with the empire. Not to mention at this time the holy roman empire (HRE) had a large controversy, where people wondered if the catholic church of the HRE had the right to appoint clerics and other church officials.
This all lead to an increase in care in religion and with propaganda of a "just war" being spread around by the Papacy the war was inevitable.
After the II war, the African Nationalism emerged late 1940s and early 1950s because three main reasons: The first one was that nearly two million African soldiers who were part of the II war (1939-1945) were discontent after coming back to the colonial states to be treated as slaves. The second reason was that Kwame Nkrumah father of the Pan Africanism, influenced the African Nationalist leaders against the colonial rules to reach freedom and finally the third reason was to maintain the unity among them after the rejection of colonies which oppressed African Nationalist.
Isaac Newton promoted the idea that science must rely on repeated observation and experimentation.
Answer:
so we learn from others and dont repeat the same mistakes as they once did
