How did the Incas create this city in the clouds

What role did the alliance system play in preventing austria-hungary and serbia from coming to a compromise settlement?

Which 19th century technological advancement would best allow farmers along the mississippi river in iowa to quickly transport their crops to buyers in louisiana?

Why did trade along the silk road increase after it fell under mongol control? o people stopped using camels the mongols paved the road o it became safer to travel the mongols were better traders next question ask for