Why was andrew jackson called old hickory?

Andrew Jackson's soldiers in the war of 1812 gave him the nickname "Old Hickory" because they said he was as tough as the wood of a hickory tree.

1. it was caused by feudalism

2. charlemagne used christianity as a major cornerstone for his rule. cloisters were built all over the empire to act as centers for the (re)population of the vast european wilderness.

3. the europeans feared the next raid every time chetak

i'm not so sure about #6. but i hope i you with the first 3.

me on my last question.