The best kind of cinnamon comes originally from an island south-east of India called Sri Lanka. It's the inner bark of a small tree that grows there. There's a more common kind, that most people think isn't quite as good, that grows wild all over China and other parts of East Asia (it's the Chinese kind that we mostly get in the United States). We know that people were using cinnamon on their food at least as early as 2700 BC, when Chinese texts first mention it.
Because cinnamon doesn't grow in West Asia, Europe or Africa, people from those places imported cinnamon from India and East Asia. People in West Asia were probably using cinnamon by about 1000 BC - the Bible mentions cinnamon as one of the spices Moses used. Cooks valued cinnamon because it helps to preserve food and keep it from going bad.
The Egyptians, the Greeks, and the Romans were willing to pay a lot of money for cinnamon. In the Middle Ages, a lot of the wealth of the Abbasid Empire, and of the Italian republics like Genoa and Venice, came from taxes on cinnamon being brought from India through the Abbasid Empire to Europe and North Africa. The Crusades made more Europeans familiar with cinnamon and so more and more people wanted it.
But when the Mongol Empire collapsed after the Black Death in the 1300s AD, traders stopped traveling east and west along the Silk Road. The price of cinnamon went up, and Europeans began to look for another way to get cinnamon by exploring around the coast of Africa and sailing over the Atlantic.
To find out more about Indian food, check out these books from your local library or from Amazon:
Cooking the Indian Way, by Vijay Madavan (2002). Written for middle schoolers, with an emphasis on low-fat and healthy meals.
Land of Milk and Honey: Travels in the History of Indian Food, by Chitrita Banerji (2002). Not a cookbook, but a discussion of Indian food, for grown-ups.
Eyewitness India, by Manini Chatterjee (2002). Written for kids.
The Spice Route: A History, by John Keay (2006). For adults, but a good account of the spice trade (California Studies in Food and Culture).