The first Crusade was started because

When the Seljuk Turks took control of the Holy Land, it became more dangerous for Christians to travel there" would be the best option, since most of the Crusades were largely about "taking back the Holy Land

the hyksos invasion. the hyksos were able to attack egypt successfully because of their skills in using bronze weapons, composite bows and the use of the horse and chariot during the invasion. although the egyptians depict a barbarian-type overthrow, the truth is the seizure was likely a relatively peaceful one.

a big wall across the mexican border so no drugs, terrorist, or illegal immigrants can come through : )