Around 1840 hope this helps! :)
It is taught in school because it has to do with the world around us and it affected our country.
For the Louisiana purchase question, it more than doubled the size of the united states. As for the second question I believe the answer would be "Thomas Jefferson was eager to explore the west to ensure the survival and prosperity of the United States"
1. It enabled the Chinese people to navigate the seas and participate in sea trade.
2. It inspired China to expand its army and conquer more territory.
