How did the conclusion of the Crusades and weakening of the Holy Roman Empire in the 13th century affect the Ottoman Empire?

What motivated germany to make an alliance with austria-hungary?   a.  fear of aggression from the united states      b.  fear of aggression from france      c.  the desire to invade russia      d.  fear of aggression from england

What event brought the us into wwii? what conflicts happened after the us entered the war? i know the first part of this question, i need with the second part.

Were african-americans allowed to serve in the military in wwi?