why do they call pennsylaviana the keystone state?

Question

why is penn.the keystone state?

Answer 1

Because the Declaration of Independence was signed here, in Pennsylvania (it's in Philadelphia)
It was the keystone on the building of the nation.

(A keystone is an important stone in buiding a building)

Answer 2

Pennsylvania has also been known as the Keystone State since 1802,[7] based in part upon its central location among the original Thirteen Colonies forming the United States.[7] It was also a keystone state economically, having both the industry common to the North, making such wares as Conestoga wagons[8] and rifles,[9] and the agriculture common to the South, producing feed, fiber, food, and tobacco.[10]

Answer 3

please see the fallowing web
1.www.assetprotection.book.com
2.www.theonion.com
3.www.drivingvotes.org
4.www.nationalreview.com
5.www.pgc.state.pa.us
6.www.funtrivia.com