Why is the Louisiana Purchase known as one of Thomas Jefferson's greatest accomplishments as president?

The acquisition of this new territory doubled the size of America. Jefferson was able to buy the land from the French for less than $0.03 per acre due to hardships the French were facing: a slave revolt in Haiti, a probable war with Great Britain, and financial difficulties. Americans swiftly began moving westward, which later resulted in new states joining the Union.

Which sentence has correct grammar: 1) Alexandra, who loves to cook, has invited everyone over for dinner. 2) Alexandra, whom loves to cook, has invited everyone over for dinner. 3) Alexandra, that loves to cook, has invited everyone over for dinner.

1) Alexandra, who loves to cook, has invited everyone over for dinner.

When did the Medieval period began and how long did it last?

The Medieval period roughly began around 400 AD - 500 AD, after the fall of the Roman Empire, and lasted until the early years of 1500 AD.