You didn't really provide the letter out of which we should be able to deduce the benefits. However, Crusaders would say that the benefit of the crusaders were that they regained the holy land and could also profit out of this either by looting and pillaging neighbouring muslim villages or because they thought they were closer to God this way.
People had to learn how to make irrigation ditches for their crops to get enough water.
German accents. And Jewish slaves
Because of the sugar plantations in the Caribbean needed lots of maunel labor