One historical event or development in the period 1800 to 1823 that could be used to support Cunningham's interpretation is the Louisiana Purchase.
The Louisiana Purchase in 1803 is said to be a significant acquisition by the United States, under President Thomas Jefferson, doubled the country's territory. The expansion westward is one that could be linked to Cunningham's emphasis on territorial growth as a key driver of American identity.
So, The acquisition of vast land brought new opportunities, resources, and challenges, is known to be influencing the nation's evolving identity and setting the stage for the pursuit of manifest destiny.